Abstract: There is provided a method and a device of monitoring oil oxidation in real time. The method of the present invention comprises the steps of: irradiating ultraviolet light into oil to be monitored; measuring fluorescence emission intensity of the oil in red, green and blue wavelength bands; determining one value measured in a relatively long wavelength band and the other value measured in a relatively short wavelength band among the fluorescence emission intensity measured in the red, green and blue wavelength bands; calculating a fluorescence emission ratio which is defined as a ratio of the value measured in the relatively long wavelength band to the value measured in the relatively short wavelength band; and monitoring a change in the fluorescence emission ratio. It is then determined whether the fluorescence emission ratio reaches a predetermined critical magnitude. When the fluorescence emission ratio reaches the critical magnitude, the necessity of replacing the oil with new one is indicated.