Background <p>Weight stigma internalization among postpartum women may differ from other populations owing to childbirth, breastfeeding, and postnatal physical recovery. Two instruments to assess the concept of weight stigma internalization—the Weight Self-Stigma Questionnaire (WSSQ) and the Weight Bias Internalization Scale (WBIS)—have not been validated in postpartum women. This study aims to evaluate and compare the reliability, factor structure, and concurrent validity between the WBIS and WSSQ in Chinese postpartum women.</p> Methods <p>A total of 476 postpartum women (mean age 30.96 ± 4.67 years) completed the WSSQ and WBIS, as well as other relevant measures regarding perceived weight stigma, psychological outcomes, and eating behaviors. Height and weight were used to calculate the body mass index (BMI). Statistical analyses were performed using internal consistency analysis, confirmatory factor analysis, and correlation analysis.</p> Results <p>Both the WSSQ and the WBIS were found to have excellent internal consistency. In addition, both were associated with postpartum BMI, perceived weight stigma, adverse psychological outcomes, and restrained and emotional eating behaviors. Differently, the two-factor structure of the WSSQ was supported among postpartum women, but the one-factor WBIS was not.</p> Conclusion <p>The WSSQ is a reliable and valid measurement tool for assessing weight stigma internalization in postpartum women. The structure of WBIS requires further validation and modification in future research.</p>