Background: The present study investigated the relationship between spousal support during postpartum period and the sexual function and sexual quality of life among lactating women. Methods: A cross-sectional study was carried out from October to March 2021 comprising 301 breastfeeding women referred to comprehensive health centers in Qazvin, Iran. The sampling method was performed in two stages. First, via cluster sampling, ten comprehensive health centers were randomly selected. Then based on the list of lactating mothers, 31 mothers in each center were randomly selected and invited to complete the survey. The survey included three psychometric instruments (i.e., Postpartum Partner Support Scale [PPSS], Female Sexual Function Index [FSFI] and Sexual Quality of Life-Female version [SQOL-F]) as well as a reproductive and demographic information questionnaire. The findings were analyzed using univariable and multivariable regression models at a significance level of p<0.05. Results: The participants had a mean age of 30.33 years and a mean length of marriage of 7.99 years. A total of 219 women were exclusively breastfeeding (72.8%), and 82 used a combination of breastfeeding and formula milk to feed their infants (27.2%). The mean (standard deviation) scores in the postpartum period were 61.34 out of 80 (SD=11.41) on the PPSS, 86.52 out of 108 (SD=19.68) on the SQOL-F, and 22.78 out of 36 (SD=6.20) on the FSFI. Based on adjusted multivariable regression models, spousal support in the postpartum period was a significant predictor of sexual quality of life (β=0.39, p<0.001) but not a significant predictor of sexual function. Sexual quality of life was a significant predictor of sexual function (β=0.44, p<0.001). Conclusion: Given the importance of spousal support during the postpartum period in relation to sexual quality of life and sexual function, designing and implementing counseling programs based on the role of spousal support during postpartum sexual life would be helpful.