Background: Over the last decade, Iran has experienced a declining birth trend. Identifying the proximate determinants of fertility intentions among married women is informative for population studies. This study aimed to examine the importance of three immediate antecedents of fertility intention. Methods: We invited 1,100 married women to complete a well-validated questionnaire based on the theory of planned behavior (TPB). The sampling framework consisted of visitors attending hospitals in two cities in southeastern Iran. Intention for having children was measured using the item “Do you intend to have a/another child during the next 3 years?” Attitude, subjective norms, and perceived behavioral control were measured using eight, three, and three items, respectively. Structural equation modeling was used to specify the model and to test the predictive ability of the TPB constructs. Results: The response rate was 90.7% (N=998), and the mean±standard deviation age of the respondents was 34.8±7.4 years. More than 50% of the respondents reported intending to have a child in the next 3 years. All three TPB model constructs showed significant associations with fertility intentions. The standardized beta coefficients for attitudes, subjective norms, and perceived behavioral control were 0.74, 0.41, and 0.55, respectively. Conclusion The TPB model showed that psychological mechanisms play an important role in predicting the childbearing intentions of married women in Iran. Of the three TPB constructs, attitude was the strongest predictor of the intention to have a child.