An attempt was made to measure the degree of natural sun-tanning among the hybrid subjects of the Elizabeth Sanders Home, Japan. The skin reflectance was measured on 69 males and 37 females, 7 to 14 years of age, in March and in September of the same year using the Photovolt photoelectric reflection meter.Although the absolute decrease in the skin reflectance during summer tended to correlate positively with the initial degree of lightness of the skin, the relative decrease as a percentage of the initial reflectance indicated a reverse tendency : the subjects of the 'negroid' origin indicated an increased darkening of the skin compared with the other subjects. In the chromaticity diagram, a tendency of increasing saturation was found for the skin-colour change through sun-tanning The significance of the data was briefly discussed.