Abstract: Objective To investigate the photobiologic reactivity in lupus erythematosus （LE） patients and to explore the relationship between photosensitivity and the state of the illness. Methods The minimal erythema dose （MED） for ultraviolet A （UVA） and ultraviolet B （UVB） was measured by SUV1000 type ultraviolet simulator in 41 LE patients. The relationship between phototesting results and the history of photosensitivity, state of illness and immunological parameters was also evaluated for these patients. Results A lowered UVA-MED and/or UVB-MED was found in 46.34% （19/41） of these patients. Of the 19 patients, 11 were sensitive to UVA, 5 to UVB, and 3 to both UVA and UVB. The erythema persisted for 2 weeks or more in 19 patients after the irradiation of 2 - 4 folds of MEDs of UVA or UVB. The incidence of anti- Ro/SSA antibody in phototesting-positive and negative patients was 52.63% and 9.09% respectively （P = 0.001）. No significant association was found between the phototesting results and history of photosensitivity, state of illness, incidence of anti-Ro/SSA antibody or other immunological parameters. Conclusions UVA and UVB may both participate in the development of LE. MED determination may benefit the judgement of photosensitivity in LE. There is a close association between anti-Ro/SSA antibody and photosensitivity in LE.