A system for monitoring an oil concentration in a lubricoolant mixture for a machine tool comprising: - a machine tool; - a recovery tank containing a lubricoolant mixture comprising at least one lubricoolant oil, the machine tool being configured to withdraw the lubricoolant mixture directly from the recovery tank; - a detection unit configured to generate at least one measure signal; - a processing unit located outside the recovery tank; and - a wiring connecting the detection unit and the processing unit, the processing unit being configured to receive said at least one measure signal through the wiring and to digitize it; - said detecting unit comprises means (4, 5) for measuring a concentration of the at least one lubricoolant oil in the lubricoolant mixture, which are configured to generate a first measure signal representative of the measure of said concentration, characterized in that said detection unit is submerged in the lubricoolant mixture within the recovery tank of the machine tool and said detection unit comprises: - a U-shaped sealed enclosure having two legs with inner faces, which are defined by first and second mutually opposed and facing walls (9A, 9B), a detection seat being defined between said two legs for containing a predetermined volume of the lubricoolant mixture, said enclosure having two transparent elements (4A, 5A) associated with the first and second walls (9A, 9B) respectively, - a laser which is housed in the U-shaped sealed enclosure behind the transparent element of the first wall, and is configured to emit an infrared radiation, and - a photodiode housed in the U-shaped sealed enclosure behind the transparent element of the second wall, the photodiode being configured to absorb the infrared radiation emitted by the laser outcoming from said predetermined volume of the lubricoolant mixture and to generate the first measure signal as a function of the infrared radiation that has been absorbed. - a machine tool; - a recovery tank containing a lubricoolant mixture comprising at least one lubricoolant oil, the machine tool being configured to withdraw the lubricoolant mixture directly from the recovery tank; - a detection unit configured to generate at least one measure signal; - a processing unit located outside the recovery tank; and - a wiring connecting the detection unit and the processing unit, the processing unit being configured to receive said at least one measure signal through the wiring and to digitize it; - said detecting unit comprises means (4, 5) for measuring a concentration of the at least one lubricoolant oil in the lubricoolant mixture, which are configured to generate a first measure signal representative of the measure of said concentration, characterized in that said detection unit is submerged in the lubricoolant mixture within the recovery tank of the machine tool and said detection unit comprises: - a U-shaped sealed enclosure having two legs with inner faces, which are defined by first and second mutually opposed and facing walls (9A, 9B), a detection seat being defined between said two legs for containing a predetermined volume of the lubricoolant mixture, said enclosure having two transparent elements (4A, 5A) associated with the first and second walls (9A, 9B) respectively, - a laser which is housed in the U-shaped sealed enclosure behind the transparent element of the first wall, and is configured to emit an infrared radiation, and - a photodiode housed in the U-shaped sealed enclosure behind the transparent element of the second wall, the photodiode being configured to absorb the infrared radiation emitted by the laser outcoming from said predetermined volume of the lubricoolant mixture and to generate the first measure signal as a function of the infrared radiation that has been absorbed.