Adequate weight gain in pregnancy is essential for the health of the mother and developing fetus. However, a woman’s self-beliefs regarding body shape and weight gain may become a driving force toward unnecessary die- tary restriction during pregnancy. In order to assess the current status of self-beliefs, attitudes toward pregnancy related changes, and dieting behavior in pregnant women, a questionnaire survey was conducted at a prenatal clinic in Tokyo. A self-administered questionnaire was distributed to 500 women and 248 women responded with eligible data. Nearly all respondents (91.5%) stated that they knew their own weight gain targets. Thirty- four women (13.7%) reported dieting before being pregnant, and 88 women (35.5%) reported current dieting. Seventy-eight of the current dieters were doing so based on self-judgment, and only fifteen were following a di- etician’s advice. The majority of the respondents (69.0%) believed that smaller babies would help a smooth de- livery. From multivariable logistic regression analysis, the odds ratio (OR) for current self-judged dieting was significant in women who had dieted before pregnancy (OR: 4.67, 95% confidence intervals (CI): 2.10-10.4), and those who desired smaller babies for a smooth delivery (OR: 2.73, 95% CI: 1.35-5.52). Obstetricians, mid- wives, and dieticians should be aware of previous dieting history and self-beliefs in pregnant women, in order to give professional advice about the importance of adequate weight gains.