The prevalence of natural gastrointestinal nematodes was observed in cattle during the period from June, 2004 to May, 2005 in Sadar upazila of Mymensingh district. The prevalence of gastrointestinal nematodes was 84.1% (rainy seasons-97%, summer-85.5% and winter seasons-69.8%). The prevalence of strongyles (Haemonchus sp., Trichostrongylus sp., Oesophagostomum sp. and Mecistocirrus sp.), Bunostomum sp., Strongyloides sp., Trichuris sp. and Capillaria sp. were 63.9%, 26.3%, 21.5%, 17.3% and 24.5%, respectively. Water extracts of 20 indigenous plants(neem, tobacco plant, barbados lilac, betel leaf, pineapple, jute, turmeric, garlic, devil's tree, papaya, lime tree, dodder, white teak, conessi tree, bitter gourd, sweet basil, white verticillia, pomegranate, sage, chaste tree) showed potential in vitro activities against adult parasites. Out of these, 20 plant extracts, 10 plants (neem, tobacco, barbados lilac, betel leaf, pineapple, jute, turmeric, garlic, dodder and bitter gourd) showed 100% efficacy against adult worms, 4 plants (devil's tree, papaya, white verticillia and chaste tree) showed 90-98% and others (lime tree, white teak, conessi tree, sweet basil, pomegranate and sage) showed below 90%.