Objectives: This study examined the effect of changes in psychosocial workplace characteristics on weight gain and abdominal obesity. Methods: Twice, at an interval of 6 years, the authors conducted examinations of job demand-control-support and measurements of body mass index and waist circumference among 2200 men and 1371 women aged 30-53 years and working in a factory. The scores of the psychosocial work characteristics in each examination were dichotomized at the median values for the men and women separately and then categorized into three groups as follows: group I: low score in both the first and second examinations, group II: low score in the first examination and high score in the second (or high at the first and low at the second), and group III: high in both the first and second examinations. Results: Although there was no statistically significant association between psychosocial work characteristics and the change in body mass index, for both genders, the change in waist circumference increased more in group III than in group I. Similarly, the odds ratios for the change in waist circumference above the 75th percentile for groups II and III increased more than in group I, being 1.13 [95% confidence interval (95% CI) 0.87-1.46 and 1.39 (95% CI 1.07-1.79) for the men in groups II and III, respectively, and 1.27 (95% CI 0.90-1.78) and 1.78 (95% CI 1.26-2.52) for the women in groups II and III, respectively. Conclusions: The results suggest that high job strain is a risk factor for increased abdominal obesity.