Background: Birth weight is the single essential factor determining the survival, growth, and rndevelopment of infants. LBW is defined by the WHO as weight at birth less than 2500 gram,rnwhile very LBW is considered as a; birth weight less than 1500gram, on the other hand veryrnextremely LBW a; birth weight less than 1000gram, regardless of gestational age. Pregnancyrnafter the age of 35 confers risk to both child and maternal health it has been broadly documented.rnIn particular, positive association between old maternal age and risk of LBW and preterm birth.rnNeonatal mortality is 20 times higher among LBW babies compared to their counterparts.rnObjective: To assess the prevalence of LBW born to older women and its risk factors in AddisrnAbaba, Ethiopia 2020. rnMethod: Institutional based cross-sectional study was conducted from Oct 2019 to DEC 2020, inrnAddis Ababa, Ethiopia. A total of 625 old age women delivered in health institutions werernselected by using systematic random sampling. Data were collected using an intervieweradministeredrnrnstructured questionnaire. The collected data were coded and entered into therncomputer using Epi Data version 3.1 and the data were analyzed using STATA version 15rndescriptive statistics was carried. In addition binary logistic regression model was used torndetermine the association between different factors and low birth weight. Finally, adjusted oddsrnratio results from a multivariate logistic regression were used to measure the strength, direction,rnand significance of the association between the different independent variables and low birthrnweight, the dependent variable. The level of significance was decided to be when p < 0.05, thatrngiven a 95% confidence interval for the test statistic.rnResult: The prevalence of low birth weight was found to be 15.04 % (95% CI 12.4-18.1). Age ofrnthe mothers (40-49 years) [AOR=[AOR=3.16: 1.06, 9.46]], low-income status [AOR=4.33:1.24,rn15.19], mothers who had mid-upper arm circumference less than 23cm [AOR=4.49:1.26,16.02],rnmothers who gave birth before 37 weeks gestational age [AOR=6.87:2.76,17.07], mothers whornhad a previous abortion history [AOR=4.22:1.45,9.66] and those who had pregnancy-inducedrnhypertension [AOR=5.80:2.23, 15.18] were more likely associated with low birth weight. rnConclusion: The prevalence of low-birth-weight is high compared with national studies amongrnelderly mothers. Age group, monthly family income, mid-upper arm circumference, gestationalrnweek, history of abortion and pregnancy induce hypertension were found to be significantlyrnassociated with LBW.