Background: Anti-retroviral therapy has made a significant reduction in morbidity and mortality related to HIV/AIDS. However, it cannot be fully realized without addressing barriers related to retention in care and medication adherence. The roll out of simplified Option B+ was launched in Ethiopia in 2013 with the aim of eliminating new HIV infection in children in 2015 and to keep the mother alive. Objective: To assess levels of option B+ adherence and associated factors among pregnant women on PMTCT follow-up at public health facilities of the East Shawa zone, Ethiopia Methods and materials: The study was conducted in public hospitals and health centers in East Shawa zone from January to June 2017. A descriptive cross-sectional study design was implemented to select 304 pregnant women using a systematic random sampling method. Data were collected using a structured and pre-tested questionnaire; the collected data were cleaned and entered into SPSS Version 21 for analysis. Multivariate logistic regression was used to determine association between independent and dependent variables. Result: Two hundred ninety-three pregnant women who were on option B+ participated in the study. The mean ages and standard deviation of the participants were 29.2 ± 4.6. The overall ART adherence of pregnant women on ART medications was 82.6%. The study showed that participants educational status, AOR 4.54(95% CI; 1.72-11.95), participants status disclosure 2.61(95% CI; 1.01-6.71), social and financial support to the participants AOR 2.76(95% CI; 1.17-6.51), counseling on the benefit AOR 2.9(95% CI; 1.27-6.63), were all positively and significantly associated with adherence to option B+ treatment while experience of drug side effect AOR 0.24(95% CI; 0.1-0.6), and fear of stigma and discrimination AOR 15.79(95% CI; 4.64-53.67), were negatively associated with adherence to option B+ treatment. Conclusion and recommendation: While education, counseling on health benefit of treatment for the fetus and the mothers, social and financial support favors adherence, Fear of stigma and discrimination and drug side effects effect negatively affect adherences to option B+ among pregnant women attending PMTCT in public health facilities. The investigator recommends collaborative work among patients, healthcare professionals, and public to enhance ART adherences Key word: HIV, ART, Option B+, Adherence, pregnant women, Ethiopia