A large number of compounds found naturally in plants have received increasing attention because of their interesting biological properties and possible protective role in curing human cancer and other hormone-dependent diseases. It has been established that many plants exert their fertility/anti- fertility effects through substances known as phytoestrogens. As India''s NE region is one of the Biodiversity Hot-spots in the World, it is now high time to explore the bioactivity of its indigenous medicinal plants. One of these plants namely Careya arborea Roxb. has a very old history of traditional use as contraceptives among some groups of rural people in this region of India, therefore obviously it demanded a proper investigation.In the present investigation, the fertility/antifertility activities of the root extract of Careya arborea Roxb. were determined in vivo in albino mice of either sex. It has been found that the root extract of this plant influenced virtually every aspect of mammalian reproduction in albino mice of either sex via effects on the morphology and physiology of reproductive organs and sexual behavior.