The International Clearinghouse for Birth Defects, Surveillance and Research reports a rise in the prevalence rate of spina bifida in Japan. We determined first-trimester folate status of Hokkaido women and identified potential predictors. Participants were 15 266 pregnant women of the Hokkaido Study on Environment and Children's Health Cohort. Data were extracted from self-reported questionnaires and biochemical assay results. Demographic determinants of low folate status were younger maternal age (adjusted OR (AOR) 1.48; 95% CI 1.32, 1.66), lower educational level (AOR 1.27; 95% CI 1.17, 1.39) and lower annual income (AOR 1.11; 95% CI 1.01, 1.22). Plasma cotinine concentrations of 1.19-65.21 nmol/l increased the risk of low folate status (AOR 1.20; 95% CI 1.10, 1.31) and concentrations >65.21 nmol/l further increased the risk (AOR 1.91; 95% CI 1.70, 2.14). The most favourable predictor was use of folic acid (FA) supplements (AOR 0.19; 95% CI 0.17, 0.22). Certain socio-demographic factors influence folate status among pregnant Japanese women. Modifiable negative and positive predictors were active and passive tobacco smoking and use of FA supplements. Avoiding both active and passive tobacco smoking and using FA supplements could improve the folate status of Japanese women.