Background & Objectives: Mother ’ s milk is the best food for the newborns and has positive effects on both mother and infant health, decreasing infant mortality, satisfying emotional needs of mother and infant and economizing the domestic as well as social expenditures. Unfortunately, because of different economical, social and cultural reasons in many parts of the world breast feeding and its length of time has decreased. WHO emphasizes breast feeding in the first six months of life in developing countries. This study is an attempt to determine the causes of unsuccessful breast feeding in the first six months after birth in Ardabil.

  Methods : This descriptive analytical�study was conducted on 160 mothers who had 2- month- old or younger infants and did not have exclusive breast feeding until the end of 6 months. The researchers referred to 4 health centers, selected based on cluster sampling, in order to select the qualified mothers and complete the questionnaires in their presence.

 Results: Most of the mothers (37.5%) have begun feedings supplementary nutrition to their infants at the age of 2-4 months. The most common (90.5%) cause for the lack of the exclusive breast feeding was found to be insufficiency of mother milk.Most of the mothers (67%) stated the infant cry as the main reason for this insufficiency. There is a significant relationship between exclusive breast feeding on the one hand and the delivery, time of first feeding, occupation and mother ’ s education on the other (p<0.05).

  Conclusion : Social and economic conditions and misbeliefs have all affected the success of exclusive breast feeding. Most of these problems can be prevented through proper trainings.