PROBLEM TO BE SOLVED: To provide a biological observation system capable of improving efficiency in performing a surgical treatment for a lesioned part.SOLUTION: A biological observation system 101 includes: an illumination part for generating first illumination light whose absorption coefficient changes according to a degree of hemoglobin oxygen saturation in the blood in a predetermined wavelength band, second illumination light including a wavelength in which an absorption coefficient of oxyhemoglobin is equal to an absorption coefficient of deoxyhemoglobin in the predetermined wavelength, and third illumination light having one or more wavelength bands in a wavelength band longer than the predetermined wavelength band an image pickup part 12 an information acquisition part for acquiring the information related to a degree of oxygen saturation of a subject in the predetermined wavelength band by an inter-image computation of an image signal at a time when the first illumination light is radiated and an image signal at a time when the second illumination light is radiated and an image information generation part for generating image information that reflects the information related to the degree of oxygen saturation of the subject in the predetermined wavelength band.
