A method for evaluating an oxygen concentration in a silicon single crystal by a photoluminescence method or a cathode luminescence method, wherein the silicon single crystal is irradiated with an electron beam at a predetermined dose or an ion beam other than carbon or oxygen at a predetermined dose, intensity of an emission line (C line) derived from composite defects Ci-Oi of interstitial carbon Ci and interstitial oxygen Oi formed in the silicon single crystal and intensity of an emission line (G line) derived from composite defects Ci-Cs of interstitial carbon Ci and substitutional carbon Cs formed in the silicon single crystal are measured at a predetermined temperature, an intensity ratio of the C line and the G line (Ci-Oi intensity/Ci-Cs intensity) is determined, a carbon concentration [Cs] in the silicon single crystal is measured and the oxygen concentration [Oi] is evaluated by substituting the intensity ratio (Ci-Oi intensity/Ci-Cs intensity) and the carbon concentration [Cs] in the silicon single crystal into the following equation: [Oi]=α·(Ci-Oi intensity/Ci-Cs intensity)·[Cs] (where α is a proportionality constant), wherein when evaluating the oxygen concentration, the following is performed in advance: a test crystal which is a silicon single crystal with a known oxygen concentration and a known carbon concentration is prepared, the test crystal is irradiated with the electron beam at the predetermined dose or the ion beam other than carbon or oxygen at the predetermined dose, intensity of a C line and intensity of a G line formed in the test crystal are measured at a predetermined temperature, an intensity ratio of the C line and the G line (Ci-Oi intensity/Ci-Cs intensity) in the test crystal is determined, characterized in that a value of the proportionality constant α is determined from the oxygen concentration and the carbon concentration in the test crystal, the intensity ratio of the C line and the G line in the test crystal (Ci-Oi intensity/Ci-Cs intensity), and the equation. the silicon single crystal is irradiated with an electron beam at a predetermined dose or an ion beam other than carbon or oxygen at a predetermined dose, intensity of an emission line (C line) derived from composite defects Ci-Oi of interstitial carbon Ci and interstitial oxygen Oi formed in the silicon single crystal and intensity of an emission line (G line) derived from composite defects Ci-Cs of interstitial carbon Ci and substitutional carbon Cs formed in the silicon single crystal are measured at a predetermined temperature, an intensity ratio of the C line and the G line (Ci-Oi intensity/Ci-Cs intensity) is determined, a carbon concentration [Cs] in the silicon single crystal is measured and the oxygen concentration [Oi] is evaluated by substituting the intensity ratio (Ci-Oi intensity/Ci-Cs intensity) and the carbon concentration [Cs] in the silicon single crystal into the following equation: [Oi]=α·(Ci-Oi intensity/Ci-Cs intensity)·[Cs] (where α is a proportionality constant), wherein when evaluating the oxygen concentration, the following is performed in advance: a test crystal which is a silicon single crystal with a known oxygen concentration and a known carbon concentration is prepared, the test crystal is irradiated with the electron beam at the predetermined dose or the ion beam other than carbon or oxygen at the predetermined dose, intensity of a C line and intensity of a G line formed in the test crystal are measured at a predetermined temperature, an intensity ratio of the C line and the G line (Ci-Oi intensity/Ci-Cs intensity) in the test crystal is determined, characterized in that a value of the proportionality constant α is determined from the oxygen concentration and the carbon concentration in the test crystal, the intensity ratio of the C line and the G line in the test crystal (Ci-Oi intensity/Ci-Cs intensity), and the equation. [Oi]=α·(Ci-Oi intensity/Ci-Cs intensity)·[Cs] (where α is a proportionality constant), wherein when evaluating the oxygen concentration, the following is performed in advance: a test crystal which is a silicon single crystal with a known oxygen concentration and a known carbon concentration is prepared, the test crystal is irradiated with the electron beam at the predetermined dose or the ion beam other than carbon or oxygen at the predetermined dose, intensity of a C line and intensity of a G line formed in the test crystal are measured at a predetermined temperature, an intensity ratio of the C line and the G line (Ci-Oi intensity/Ci-Cs intensity) in the test crystal is determined, characterized in that a value of the proportionality constant α is determined from the oxygen concentration and the carbon concentration in the test crystal, the intensity ratio of the C line and the G line in the test crystal (Ci-Oi intensity/Ci-Cs intensity), and the equation. a test crystal which is a silicon single crystal with a known oxygen concentration and a known carbon concentration is prepared, the test crystal is irradiated with the electron beam at the predetermined dose or the ion beam other than carbon or oxygen at the predetermined dose, intensity of a C line and intensity of a G line formed in the test crystal are measured at a predetermined temperature, an intensity ratio of the C line and the G line (Ci-Oi intensity/Ci-Cs intensity) in the test crystal is determined, characterized in that a value of the proportionality constant α is determined from the oxygen concentration and the carbon concentration in the test crystal, the intensity ratio of the C line and the G line in the test crystal (Ci-Oi intensity/Ci-Cs intensity), and the equation.