Background: Early initiation of breastfeeding within one hour of life/birth safeguards infants from dying during the most vulnerable time in their lives. However, only 45% of newborns were put to the breast within the first hour of life in the world and 52% in Ethiopia. Objective: To assess the prevalence of early initiation of breast feeding and associated factors among mothers with children less than 12 months old in Kirkos sub city, Addis Ababa. Method: Institutional based cross -sectional study was conducted. Data were collected from March 01-30/2017 at Kirkos sub city. A sample of 377 mothers was involved in this study. Pre-tested structured questionnaire was used to collect data. The collected data were entered in to EPI-INFO software and analyzed by using SPSS version 20. Result: Overall prevalence of early initiation of breast feeding was 54.6% [95% CI: 49.1%, 59.7%]. Mothers who had husbands who works in private or nongovernmental organizations [AOR=2.57; 95% CI :( 1.218, 5.769)] were associated with increased odds. On the other hand, lack of postnatal counseling [(AOR=0.118; 95% CI :( 0.044, 0.313)], lack of family support [(AOR=0.359; 95%CI (0.132, 0.980)] and giving anything to drink for their child before breast feeding initiation [(AOR=0.014; 95% CI :( 0.003, 0.063)] were factors associated with decreased odds. Conclusion: This study showed that only almost half of infants were put to the breast within one hour of birth. Mothers who had husband working in private or non-governmental organization was a factor associated positively whereas lack of postnatal counselling, lack of family support during motherhood time and giving anything to drink for the child before breast feeding initiation were factors associated negatively with early initiation of breast feeding