This paper has analyzed the characteristic features of women's associations and problems inhibiting their effective participation in rural development projects in Osun State, Nigeria. One rural local government area was purposively selected in each of the six administrative zones in Osun State, based on high degrees of ruralness. A list of registered or formal women's associations was collected from each of the six selected Local Government Area headquarters. Snowball sampling technique and community key informants were employed to identify the non-registered or informal women's associations in the study area. Sixty women's associations (one formal and one informal from each of the 30 selected rural communities), purposively selected based on performance and availability, were interviewed by means of structured interview schedule consisting of both closed and opened ended questions (to exhaust all possibilities) duly pre tested before use. A total of 137 women's associations were identified in the study area. The popular goals of the majority were: financial assistance (96.4%), supporting members during ceremonies (95.0%), community development (86.9%), donating to the needy (69.3%), and exchange of helping hands in occupations (51.1%). A majority (53.3%) had between 21-40 members, formed before 1992 (70%), and about 50.6% and 40% disseminated information through minutes of the meetings and interpersonal contact respectively, while 43.3% claimed members' contributions as their major source of finance. About 48.3% met between 11-15 times a year, and 57.1% claimed attendance of meetings as the major responsibility of their members. The participation of the selected women's associations in rural development projects was average, with a mean of about three projects. A significant relationship was found between the participation of women's associations in the development projects of their communities and problems facing them, namely; finance (T=-2.38), tribalism (T=2.37), and lack of community supports (T=-2.39). The study concludes that women's associations are very prominent in the sampled rural areas. However, inadequate finance, tribalism and lack of community support are among the major problems inhibiting their effective participation in the development projects of their communities. (Contains 4 tables and 2 figures.)