PurposeWeight bias internalization (WBI) is significantly associated with negative physiological and psychological consequences. Given its negative effects, appropriate measurement of WBI is required for weight management and mental and physical health in people with weight problems. One of the most reliable and frequently used questionnaires to assess WBI is the Weight Self-Stigma Questionnaire (WSSQ). However, a Japanese version of the WSSQ has not yet been developed. Thus, the current study aimed to develop a Japanese version of the WSSQ (WSSQ-J) and validate its psychometric properties in the Japanese context.MethodsA total of 1454 Japanese participants (age 34.44 ± 6.92; male = 498) with diverse weight statuses (Body mass index: 21.44 ± 3.52, 13.79–41.40 kg/m2) completed an online survey for the WSSQ-J. The internal consistency of the WSSQ-J was estimated by calculating Cronbach’s α. Confirmatory factor analysis (CFA) was then carried out to confirm that the factor structure of the WSSQ-J was the same as that of the subscales of the original WSSQ.ResultsThe WSSQ-J had a Cronbach’s α of 0.917, indicating good internal consistency. In CFA, the comparative fit index was 0.945, the root mean square error of approximation was 0.085, and the standardized root mean square residual was 0.040, indicating that the two-factor model showed satisfactory goodness-of-fit.ConclusionThis study replicated the original findings related to the WSSQ, showing that the WSSQ-J is a reliable WBI questionnaire consisting of two factors. Therefore, the WSSQ-J would be a reliable tool for assessing WBI among Japanese.Level of evidenceLevel V, descriptive cross-sectional study.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40519-023-01573-0.