Lights of different spectra were applied to bagged ‘Red Fuji’ apple fruits either attached or detached to trees in order to study the effects on the surface coloration. Anthocyanin and sugar contents and relevant enzyme activities were then analysed to study the effects of different lights on fruit coloration. Bagged fruits detatched from trees developed no red color under irradiation of both Red light and UVA (＞320nm ) and fruits were injured and turned brown under irradiation of UVA. UVB light （280-320nm）or any light combinations involving UVB significantly induced red coloration of fruit. White light had similar function of inducing fruit coloration but the effectiveness was not as significant compared with UVB light and its combinations. The activity of PAL enzyme and sugar content increased, which stimulated the accumulation of anthocyanin when the fruits are exposed to UVB light and white light. Therefore, UVB light is the direct external factor for the coloration of ‘Red Fuji’ apple and one of the light signals for stimulating fruit coloration.