A cross sectional study of knowledge, perception and sociodemographic factors affecting preventive behaviors of married employed women on HIV/AIDS was conducted in the Muang district of Nakhon Ratchasima province, Thailand from April to May 1994. The study was aimed at finding association of knowledge, perception about HIV/AIDS and ,sociodemographic factors with preventive behaviors among the married employed women working in different offices. Information concerning the study were collected by structured self-administered questionnaires from 307 married employed women in the age group 15 to 45 years having education, secondary level and higher from 3 major service sectors: Government, Semi-government and NGO/private organizations. The objective of the research was to study the knowledge , perception about HIV/AIDS and sociodemographic factors of the employed women and to find the association with their preventive behaviors. The result of the study revealed that despite their good knowledge and perception most of the respondents lacked preventive behaviors. No significant association of knowledge and perception about HIV/AIDS with the preventive behaviors could be found. It was observed that high education and high income group of women had higher role in sexual decision making, significant association of sexual decision making was found with education and income of the respondent. The study concludes that: 1. Knowledge and perception alone can not be considered as an influencing factor of preventive behaviors against HIV/AIDS. 2. Education and income of married employed women have significant role in influencing sexual decision making and discouraging risk behaviors of their husbands.