Objective To study the effect of PM2.5 combined with UVB treatment on human keratinocytes HaCaT. Methods The PM2.5 in the air was collected in Guangzhou and the metal ingredients were analyzed. The cells were divided into four groups:negative control group(NC group),simple PM2.5 treatment group with the concentration of IC50(PM2.5 group),simple UVB irradiation group with the dose of 30 mJ/cm2(UVB group)and PM2.5 combined with UVB treatment group(combined treatment group). The effects of different treatments on cell viability were measured by MTT assay and those of different treatments on apoptosis were detected by flow cytometry. The expressions of PARP and LC3 protein were detected by Western blot. Results The metal components in PM2.5 samples included Ca ,Zn ,Ba ,Al ,Cu ,Pb ,etc. After the treatment of PM2.5 on HaCaT cells ,we concluded that the IC50 was about 300 μg/mL. The inhibitory effect on cell viability after 24 h in different groups showed significant difference (P < 0.001) and the viability of the combined treatment group was the lowest (P < 0.001). Flow cytometry analysis showed that compared with that of NC group,the apoptosis rate of PM2.5 group(P < 0.01),UVB group(P < 0.01)and the combined treatment group(P < 0.01)increased,but the apoptosis rate in the combined treatment group was higher than that of PM2.5 group(P < 0.05),but lower than that in UVB group(P < 0.01). Western blot showed that the level of LC3-Ⅱ and PARP in another three groups was higher than that of NC group;PARP in the combined treatment group was lower than that in UVB group and LC3-Ⅱ increased compared with that in PM2.5 and UVB group. Conclusion PM2.5 can increase the harm of UVB on HaCaT cells and the main mechanism may be through increasing autophagy rather than apop-tosis.