Abstract: Objective To observe the expressions of senescence-associated biomarkers in fibroblasts after repeated exposures to subtoxic doses of ultraviolet B （UVB）, and to study the effect of ginsenoside Rb1 and Rg1 as well as Lycium barbarum polysaccharide on the UVB-induced premature senescence and on the expressions of senescence-associated signals including p16, p21 and p53. Methods Skin fibroblasts were classified into 8 groups to receive pretreatment with traditional Chinese medicine （TCM） monomers only, UVB irradiation only, no treatment, or both pretreatment and irradiation. UVB was given successively at a dose of 15 mJ/cm2 for 10 times, and the concentration of three monomers was 50 mg/L. After 5 days of treatment, light microscopy was used to observe the morphology of fibroblasts, transmission electron microscopy to study the cell ultrastructure, β-galactosidase histochemical staining to detect senescent cells, flow cytometry to analyze cell cycle, and RT-PCR to measure the mRNA expressions of p16, p21 and p53 in these skin fibroblasts. Results None of the 3 monomers had any effect on cell morphology, β-galactosidase activity, cell cycle or the mRNA expression of p53, p21 and p16 in skin fibroblasts. After UVB irradiation, some changes occurred to cell morphology and ultrastructure; 91.5% of the cells were stained positively for β-galactosidase. The proportion of cells in G1 phase was 88.63% ± 4.67% in irradiated fibroblasts, significantly different from that in untreated controls （49.18% ± 5.53%, P < 0.05） and that in irradiated fibroblasts pretreated with ginsenoside Rb1 and Rg1 as well as Lycium barbarum polysaccharide （71.04% ± 1.64%, 70.38% ± 2.58%, 80.09% ± 3.46%, all P < 0.05）. Compared with untreated fibroblasts, the mRNA expression of p53, p21 and p16 significantly increased in irradiated fibroblasts （P < 0.05）, however, the induced increase in the mRNA expression of p16 was inhibited by all the three monomers （all P < 0.05）, that of p21 by ginsenoside Rb1 and Rg1 （P < 0.05）, and that of p53 by ginsenoside Rb1 and Lycium barbarum polysaccharide （both P < 0.05）. Conclusions Ginsenoside Rb1, Rg1 and lycium barbarum polysaccharide can inhibit UVB-induced premature senescence, which may be associated with the down-regulation of mRNA expressions of p16, p21 and p53.

Key words: Ultraviolet