An apparatus for estimating a biological substance in a user using a unit spectrum for the biological substance acquired using a biological tissue simulation solution is provided. The apparatus may include a spectrometer configured to emit a light to a skin of a user, detect the light returned from the skin, and measure a skin spectrum of the user from the detected light and a processor configured to estimate a biological substance in the user based on the measured skin spectrum and a unit spectrum acquired using a biological tissue simulation solution.
