A non-invasive optical method for in vivo determination of the concentration of carotenoid antioxidant substance lycopene in the skin, based on resonance Raman spectroscopy, is presented. The Ar⁺ laser with an excitation wavelength at 514.5 nm was used, which corresponds to the maximum of the absorption of lycopene. This wavelength excited more lycopene than other carotenoids, because of the different absorption spectra of the carotenoids in the green spectral range. The absence of the reabsorption of carotenoids at the present wavelength and the elimination of the influences of heterogeneities of the skin, such as microstructure and pigmentation on Raman measurements by the use of a broad excitation laser beam, allows lycopene to be measured at a high accuracy. The utilization of the measurements of back reflected light from the skin allowed measurements to be performed on volunteers with all skin types.