Background: Human immunodeficiency virus (HIV) is an etiologic agent of AIDS in human.rnVertical transmission among women who had no access to ARV treatment was estimated to be15-20% in Europe, 25-30% in America and 25-35% in Africa. Vertical transmission is one of thernmodes of HIV transmission with the rate of 10% in Ethiopia.rnObjective: The aim of this study was to determine the proportions and time of MTCT of HIV-1rnand to evaluate the efficacy of ARV/ HAART on prevention of MTCT of HIV-1 in the studyrnareas.rnMethods: Prospective cohort study design was conducted from November, 2011 to May 22,rn2012. A convenient sampling technique was used to recruit the study participants. 24 nonbreastfeedingrnrnand 57 breastfeeding mother-infant pairs were involved in this study. Maternalrnvenous blood and infant dried blood spot were collected; then, processed in Adama Regionalrnlaboratory. Maternal socio-demographic data were collected by using structured interviewerrnadministered questionnaire. All data were entered into Epi Info version 3.5.1 computer softwarernand descriptive analysis was performed. Then, data were exported to SPSS version 16 computerrnsoftware for statistical analysis.rnRESULTS: Five infants were infected with HIV at the end of this study. The overall rate ofrnvertical transmission of HIV was 6.2%. Maternal viral load at delivery was independentlyrnassociated with both in utero and intra-partum transmission; (OR=27.0, (95%CI, 3.5-210,rnp=0.001). In addition maternal viral load at 6 weeks of birth and low infantsâ€™ birth weight werernstrongly associated with intra-partum transmission among breastfeeding mothers, OR=25.5,rn(95%CI, 1.14-572, p=0.04, OR=29.6, 95%CI, 3.2-273, p=0.004); respectively. There were 40%rnMTCT of HIV among non ARV drug users and only 3.9% among those used ARV drugs duringrntheir current pregnancy.rnConclusion: strategies planned to reduce maternal viral load during pregnancy can be successfulrnin substantially reducing vertical transmission of HIV. In addition, other contributing factors forrnMTCT of HIV-1 should be controlled.