A method for evaluating thermal expansion properties of a titania-containing silica glass body, comprising: a measurement step of each non-destructively measuring, for the titania-containing silica glass body, a physical parameter that fluctuates depending on a titania concentration and a physical parameter that fluctuates depending on a fictive temperature, at a predetermined temperature Tx, to obtain measured values of a plurality of physical parameters; a calculation step of calculating a coefficient of thermal expansion of the titania-containing silica glass body and a slope of the coefficient of thermal expansion of the titania-containing silica glass based on the measured values of the plurality of physical parameters obtained, respectively by using a linear relational expression expressed by the plurality of physical parameters; and an evaluation step of evaluating the thermal expansion properties of the titania-containing silica glass body based on the calculated coefficient of thermal expansion, CTE, and/or slope of the coefficient of thermal expansion, CTE-SLOPE, wherein the linear relational expression to calculate the coefficient of thermal expansion is the following linear relational expression α: CTE at Tx = a 1 A + b 1 B + c 1 C + d 1 and wherein the linear relational expression to calculate the slope of the coefficient of thermal expansion is the following linear relational expression β: CTE − SLOPE at Tx = a 2 A + b 2 B + c 2 C + d 2 wherein, in the linear relational expressions α and β, is a term containing a longitudinal wave sound velocity V L or a transverse wave sound velocity Vs in the titania-containing silica glass body; is a term containing I 1 /I 0 or I2/I0 when a peak intensity at 440 cm -1 or 820 cm -1 is denoted by I 0, a scattered peak intensity at 495 cm -1 is denoted by I 1, and a peak intensity at 605 cm -1 is denoted by I 2, in a Raman spectrum in the titania-containing silica glass body; is a term containing I3/I0 or I 4 /I 0 when the peak intensity at 440 cm -1 or 820 cm -1 is denoted by I 0, a peak intensity at 960 cm -1 is denoted by I 3 and a peak intensity at 1,140 cm -1 is denoted by I 4, in the Raman spectrum in the titania-containing silica glass body; and a1, b1, c1, d1, a2, b2, c2, and d2 are coefficients calculated by regression calculation by a least-square method from the relational expressions α and β. a measurement step of each non-destructively measuring, for the titania-containing silica glass body, a physical parameter that fluctuates depending on a titania concentration and a physical parameter that fluctuates depending on a fictive temperature, at a predetermined temperature Tx, to obtain measured values of a plurality of physical parameters; a calculation step of calculating a coefficient of thermal expansion of the titania-containing silica glass body and a slope of the coefficient of thermal expansion of the titania-containing silica glass based on the measured values of the plurality of physical parameters obtained, respectively by using a linear relational expression expressed by the plurality of physical parameters; and an evaluation step of evaluating the thermal expansion properties of the titania-containing silica glass body based on the calculated coefficient of thermal expansion, CTE, and/or slope of the coefficient of thermal expansion, CTE-SLOPE, wherein the linear relational expression to calculate the coefficient of thermal expansion is the following linear relational expression α: CTE at Tx = a 1 A + b 1 B + c 1 C + d 1 and wherein the linear relational expression to calculate the slope of the coefficient of thermal expansion is the following linear relational expression β: CTE − SLOPE at Tx = a 2 A + b 2 B + c 2 C + d 2 wherein, in the linear relational expressions α and β, is a term containing a longitudinal wave sound velocity V L or a transverse wave sound velocity Vs in the titania-containing silica glass body; is a term containing I 1 /I 0 or I2/I0 when a peak intensity at 440 cm -1 or 820 cm -1 is denoted by I 0, a scattered peak intensity at 495 cm -1 is denoted by I 1, and a peak intensity at 605 cm -1 is denoted by I 2, in a Raman spectrum in the titania-containing silica glass body; is a term containing I3/I0 or I 4 /I 0 when the peak intensity at 440 cm -1 or 820 cm -1 is denoted by I 0, a peak intensity at 960 cm -1 is denoted by I 3 and a peak intensity at 1,140 cm -1 is denoted by I 4, in the Raman spectrum in the titania-containing silica glass body; and a1, b1, c1, d1, a2, b2, c2, and d2 are coefficients calculated by regression calculation by a least-square method from the relational expressions α and β.