Background and Objective: Given the importance of maternal mood in the postpartum period, which can have profound effects on maternal health, and to identify factors that can affect postpartum depression symptoms, the present study aimed to investigate the relationship between postpartum depression and maternal attachment style, considering the moderating role of spousal support. Materials and Methods: The research design was a descriptive correlational and fundamental study. The sample size consisted of 237 mothers residing in Tehran, with a maximum of 24 months passed since their childbirth. Sampling was done using the convenience method. Data were collected using the Edinburgh Postnatal Depression Scale, the Experiences in Close Relationships-Revised questionnaire, and the Reflective Functioning Questionnaire. Finally, the data were analyzed using Pearson correlation and path analysis. Results: The results showed that maternal anxious and avoidant attachment styles had a direct, positive, and significant effect on postpartum depression (P<0.01, r=0.96 and r=0.34, respectively). Additionally, spousal support had a negative and significant relationship with postpartum depression symptoms (P<0.01, r=-0.41). The coefficient obtained for the indirect effect of maternal anxious and avoidant attachment styles on postpartum depression symptoms, with the moderating role of spousal support, indicated that this effect was not significant. Conclusion: The results of this study indicate that the quality of maternal attachment is a strong predictor of postpartum depression, and spousal support cannot moderate the effects of insecure maternal attachment.