Objectives : To evaluate the association between working conditions and adverse pregnancy outcomes in Korea. Methods : We obtained data on health history, lifestyle, housework and Working conditions, such as shift work, hours standing, working time, job demand, lifting at work and at home, between August and September 2000, from self-reported questionnaires. A group of 344, occupationally active, pregnant women from 51 industries were studied. Of the women studied, 328 women were further interviewed by telephone between November 2000 and September 2001. Result : Compared with daytime work, shift work increased the risk for preform birth (an adjusted risk ratio of 2.74, 95% CI=1.02-2.62) and low birth weight (an adjusted risk ratio of 2.74,95% CI=1.02-2.02). A significantly increased risk was found for prolonged standing, with an adjusted risk ratio of preform births of 6.80 (95% CI=2.01-23.0). There were no significant differences in the incidence of spontaneous abortion between the occupational working conditions, with the enception of a previous history of spontaneous abortion. Conclusion : These findings suggest that maternal working conditions, such as shift work and prolonged standing, contribute significantly to preterm birth and low birth weight.