The alteration of main disaccharide units in the skin of hairless mice (HOS:Hr 1) after chronic and repeated ultraviolet light (UV) radiation was investigated using high performance liquid chromatography after labeling with 1-phenyl-3-methyl-5-pyrazolone. The total amount of main disaccharide units increased by UVA irradiation at the 24th and 36th weeks in comparison with the control. At the 36th week UVA significantly increased hyaluronic acid-derived delta Di-HA (HA). Dermatan sulfate-derived delta Di 4S (DS) and chondroitin sulfate-derived delta Di-4S (CS) increased at the 36th week, although not statistically significant. The total amount of main disaccharide units was increased significantly by UVB irradiation at the 24th week as compared with the control. Concerning the compositional change in main disaccharide units after a 36-week repeated exposure, the decrease in delta Di-HA(HA) and the increase in delta Di-4S (DS) were found in the order of control, UVA- and UVB-irradiated groups. These results, for the first time, indicate the precise alterations of glycosaminoglycans, both in the total amount and in the composition, confirming the previous histochemical findings. This disaccharide analysis should provide a useful method to examine the biochemical changes of skin glycosaminoglycans in photoaging.