OBJECTIVES: Thailand has been one of the leading developing countries to implement a national program to prevent mother-to-child transmission (PMTCT) of HIV. The objective of this study was to determine the impact of pharmacist intervention to monitor HIV-infected pregnant women. Pharmacist provided medication and guideline information including phamacotherapeutic suggestion. METHODS: In this research, retrospective study was employed with descriptive statistics using average percentage frequency, making use of out-patients records of treatments in HIV-infected pregnant women who informed about the benefits of taking antiretroviral (ARV) drugs for PMTCT, side effects of ARV drugs, importance of adherence to drugs and the fact that HIV transmission to their infants can possibly occur despite ARV use by pharmacist. RESULTS: The HIV-infected pregnant women group of 24 cases, 4 were withdrawn due to unable to follow up, 20 cases have been followed-up and shown the effectiveness of medicine. There were 8 new patients (33.33%) firstly received ARV. The mean CD4 cell counts at baseline of all patients were 227+-69.28 cells/mm3. Most regimens for treatment was highly active antiretroviral therapy containing zidovudine (AZT)+lamivudine (3TC)+lopinavir/ritonavir (LPV/rtv) 41.67% where treated with AZT+3TC+nevirapine were secondly used (33.33%). It was found that 34.4% of patients had adverse drug reactions. The ADR incidence of ARV was 4.0 patients and 6.2 events per 1000 person-day. Gastrointestinal system such as nausea and vomiting were found at 12.50% and 8.33% were diarrhea were the most organ system affected. During the study period, 3 patients had to change ARV regimens because of ADRs. 16.67% were non-compliance but less than 7 days at early period. The rate of MTCT of HIV was 8.33% after monitoring for one year. CONCLUSIONS: The results indicated that a medication monitoring and evaluating process by pharmacist associated with improved rational used of drug in HIV-infected pregnant women. This project provides a foundation for future quality improvement.