The aim of this study was to predict emotion regulation strategies based on negative automatic thoughts, with the mediating role of positive affect. Using a correlational design, 200 pregnant women in Yasuj(a city in Iran) were selected through convenience sampling. Data were collected using the Automatic Thoughts Questionnaire (ATQ), the Positive and Negative Affect Schedule (PANAS), and the Cognitive Emotion Regulation Questionnaire (CERQ). Regression analysis revealed that negative automatic thoughts significantly reduced positive affect (P < 0.01). Furthermore, positive affect significantly predicted both adaptive and maladaptive emotion regulation strategies (P < 0.05). While negative thoughts were associated with both types of strategies, their relationship with maladaptive strategies was stronger. In multiple regression analyses, positive affect emerged as a predictor of adaptive strategies, whereas negative thoughts predicted maladaptive strategies (P < 0.01). However, the Sobel test indicated that positive affect did not significantly mediate the relationship between negative thoughts and maladaptive strategies (P > 0.05), but it did mediate the relationship between negative thoughts and adaptive emotion regulation strategies (P < 0.01). These findings highlight the importance of managing negative thoughts in enhancing emotional regulation and suggest that boosting positive affect may help improve adaptive regulation strategies by reducing negative automatic thinking.