An oil concentration measurement system and method measure the concentration of oil over a wide concentration range and is applicable in a continuous measurement of oil concentration. A measurement-target liquid containing a known kind of oil component, absorbance spectrum is measured within a predetermined waveband where absorption of light is observed. If a predetermined criterion is met, a concentration value of the oil component is determined based on absorbance at a predetermined wavelength within the predetermined waveband and also on a first calibration curve showing relationship between the component concentration and absorbance at the predetermined wavelength. If the predetermined criterion is not met, a concentration value is determined based on the wavelength at which the absorbance has a predetermined absorbance value within the absorbance spectrum and also on a second calibration curve showing the relationship between the component concentration and wavelength at which the absorbance has the pred
