Background: The World Health Organization (WHO) recommends that mothers should initiate breast feeding within the first hour of birth and exclusively breastfed for the first six months lives. Despite the WHO recommendations of exclusive breast feeding for the first six months of life, the prevalence is remained low both in developed and underdeveloped nations. Objectives: The objective of this study was to assess the magnitude of exclusive breast feeding practices and its associated factors among mother having infants from birth to six months old in Armed Force comprehensive specialized hospital Addis Ababa Ethiopia, 2023. Method: An institutional-based cross sectional study was conducted in Armed Force Comprehensive Specialized hospital in Addis Ababa among mothers having infants from birth to six months-old from March to April 2023. Data was collected from 332 participants. All Eligible mothers who had infants from birth up to six month-old were included in the study until the calculated sample size is obtained (332). A pretested, structured interviewer- administered questionnaire was used to collect the data. Data was analysed using SPSS version 26 software. Descriptive statistics was used to present socio-demographic characteristics, and bivariate and multivariate logistic regression analysis was used to identify factors associated with exclusive breast feeding practices. Results: A total of 332 mothers were included, with a response rate of 98.7%. In this study exclusive breast feeding practice (EBF) practice was 63.7%. Mother who had postnatal follow up following their last delivery were seven times more likely to exclusively breastfeed than mothers who did not have postnatal follow up AOR: 7 (95% CI: 2.2, 22.4). Mother who delivered vaginally 13 times more likely to exclusively breastfeed their infants than those who delivered by caesarean section AOR: 13 (95% CI: 4.6, 37.5). Concerning knowledge of mothers, those who had inadequate knowledge were75% less likely to EBF than those who had adequate knowledge AOR: 0.26 (95% CI: 0.1.0.7). Conclusion: Exclusive breast feeding was practiced by almost two third of the participants. Strengthening postnatal follow up, and encouraging EBF in mothers who delivered by caesarean section are recommended.