Background & Aim: Misconceptions and misinformation about childbirth can lead to cause mood symptoms such as anxiety and depression during pregnancy, which have irreversible effects on the developmental characteristics of birth, such as birth weight or Preterm delivery. The aim of this study was to determine the effect of preparation classes about physiological childbirth in the last month of pregnancy on depression, anxiety and social support. Methods: This study was semi-experimental. The statistical population included all primary pregnant women with moderate depression in Qom city (n=186), of which 50 women were selected by simple random sampling method and randomly divided into two groups of experiment and control, with 25 women in each group. The women in experimental group participated in physiological childbirth preparation classes with their husbands, and the control group received free counseling services for six months after the study, in accordance with the ethics of research. Anxiety, depression, and social support for both groups were measured using Questionnaires of Beck's Depression Inventory, Vandenberg Pregnancy Anxiety Inventory and Mary Prosidano Social Support, after 20-weeks as Pre-test and 36weeks as post-test. Data analysis was performed using mean, standard deviation, Levin test and independent t-test with SPSS software version 20. Results: The findings showed that depression (t=22.819) and anxiety (t=10.976) were lower in the experimental group than in the control group. Also, the level of social support (t=-3233) in the experimental group was significantly higher than the control group. Conclusion: Based on the results, the training provided in physiological childbirth preparation classes was effective in reducing depression and anxiety and increasing social support during pregnancy. Therefore, using these classes can help reduce depression and anxiety of pregnant mothers and increase their social support.