Counseling services is an important component of National AIDS Control Program which aims at creating awareness and promoting changes in reducing high risk behavior against HIV/AIDS. Pregnant women attending antenatal clinics are being counseled about HIV/AIDS under prevention of parent to child transmission (PPTCT) program. The objective of this study was to assess (KABP) regarding HIV/AIDS among pregnant women attending PPTCT program before and after counseling at Lok Nayak Hospital, New Delhi. A Quasi-experimental study was conducted. Data was collected by interviewing 600 pregnant women attending ANC clinic during May 2006 to May 2007 using a pre-test and post-test interview schedule. About 69.2% of the pregnant women had heard about AIDS before the counseling. Knowledge regarding mother to child transmission of HIV was 53.5%. 38.2% knew that mother to child transmission can be reduced by drugs. The knowledge of pregnant women about AIDS was significantly different in pre-test (mean score = 15.3) and post test (mean score = 35.6) (P < 0.0001). Attitude of study participants towards people living with HIV/AIDS (PLWHA) indicated that individuals with HIV should be allowed to work (79.9%) and all commercial sex workers should compulsorily be tested for HIV (55.1%). There was significant difference between in pre-test and post-test attitude about PLWHA and HIV testing (p < 0.0001). The condom use among the study participants significantly improved after counseling (1.2% in pre-test and 58.6% after counseling) (p < 0.0001). Counseling services were effective in increasing knowledge and changes in attitude and behavior among pregnant women and the efforts needs to be sustained.