Objective To investigate the oxidative damage of ultraviolet A (UVA) radiation to primary cultured human keratinocytes and the protective effects of sunscreens from UVA Methods The levels of malondialdehyde (MDA) in supernatant and the activities of catalase (CAT) and superoxide dismutase (SOD) in intra keratinocytes were determined among primary cultured human keratinocytes irradiated by UVA radiation at different dosages The protective effects of sunscreens from UVA radiation were evaluated also Results With the dosages of UVA radiation increasing from 2 88 J/cm 2 up to 11 52 J/cm 2,the levels of MDA increased from 2 54 ?mol/L to 6 75 ?mol/L,the activities of CAT decreased from 15 76 U/mg(prot) down to 6 33 U/mg,the activities of SOD decreased from 25 55 NU/mg(prot) to 23 81 NU/mg(prot) After the primary cultured human keratinocytes were irridiated by UVA radiation with the same dosages as mentioned above through a piece of quartz glass surface of which was smeared by the broad spectrum sunscreens,the levels of MDA increased from 2 18 ?mol/L to 4 82 ?mol/L,the activities of CAT decreased from 17 19 U/mg(prot) to 10 35 U/mg(prot),the activities of SOD decreased from 26 52 NU/mg(prot) to 24 51 NU/mg(prot) Conclusion UVA radiation could cause significant oxidative damage to human keratinocytes Under the conditions of this study,the broad spectrum sunscreens had certain protective effects on keratinocytes from UVA radiation