The aim of this study is to examine the impact of lifestyle intervention on postpartum weight loss. So the investigators will have two groups in this study. In Experimental group women will receive the Healthy Lifestyle Intervention. This intervention will have been delivered during 12 weeks. In Control group women will receive general information via pamphlet about postpartum period and tips for stress management.

This study will be conducted in two phases. In the first phase , the investigators will conduct a cross-sectional study to assess factors related to the healthy lifestyle after childbirth based on the PRECEDE model. Regarding results of the study, the investigators will plan and implement a lifestyle promoting intervention and will evaluate the effect of the intervention on weight reduction among postpartum women.

Inclusion Criteria:

• Singleton pregnancy
• Lactating
• Non-smoking
• Full-term birth
• Lack of medical problems
• Lack of any pregnancy-related complications (eg, multiple pregnancy, fetal anomalies, fetal or maternal complications in current or previous pregnancy, and hypertension in pregnancy).
• Nonparticipation in other studies which may affect the results.
• 18.5≤ BMI≤29 before pregnancy
• Women who are sedentary according to the International Physical Activity Questionnaire.

Exclusion Criteria:

• Unwilling to continue participation in the study
• Pregnancy during the study
• Suffering physical problems during the study
• Smoking after birth