Background: World Health Organization recommends that breastfeeding should start within thernfirst hour of birth in term and within the first six hours for preterm by expressing breast milk. Inrnearly preterm and very low birth weight breast milk expression is an optimal solution to continuernwith breastfeeding.rnObjective: The aim this study was to assess breast milk expression practices and factorsrnaffecting it among mothers of preterm and low birth weight infants in NICUs of governmentrnhospitals in Addis Ababa.rnMethods and materials: Facility-based cross-sectional study was conducted on a total of 124rnmothers who were in NICU selected sequentially. Pretested structured questionnaire was used torncollect data and the collected data were coded, entered, and cleaned using Epidata version 4.6.0.2rnthen exported to SPSS version 26 for analysis. Odds ratios along with 95%CI were estimated tornidentify factors affecting breast milk expression practice using logistic regression analysis. Levelrnof statistical significance was declared at p-value â‰¤ 0.05. rnResults: The magnitude of late initiation of breast expression, inadequate frequency andrninadequate volume were 100%, 40.3% and 33.9% respectively. Getting instruction on method ofrntheir choice (AOR=0.55; CI=0.31 to 0.96) and gestational age â‰¤32 weeks (AOR=2.39; CI=1.34rnto 4.24) were factors significantly associated with initiation milk expression. Stable health statusrnof baby (AOR=0.11; CI=0.01 to 0.83), fair (subcritical) health status of baby (AOR=0.07;rnCI=0.01 to 0.55), were facilitators of adequate amount of milk; and worry about volume milkrn(AOR=7.50; CI=3.32 to 16.95) and worry about health status of baby (AOR=4.63; CI=2.21 torn9.70) were significantly affect the volume of expressed breast milk.rnConclusions: The present study indicated practice of early initiation of milk expression wasrnpoor. In order to promote good practice breast milk expression among mothers of preterm andrnlow birth weight inter-departmental collaboration is required.