An ecological study on soil nematodes was made in a tropical deciduous forest ecosystem. Seventeen species of nematodes were identified of whichRotylenchus sp. was the dominant plant parasitic form andAcrobeloides sp. was the dominant microbivore species. The mean annual importance value for the miscellaneous feeders, plant parasites, microbivores and predators were 57·5, 22·5, 12·6 and 7·4 respectively. The Shannon index of general divérsity was maximum during February (1·73) and minimum during June (1·41). Nematodes were distributed in clusters resulting in so called pocket effect. Of the total nematodes 88·4% occurred in the top 10 cm soil during the peak period of density and the microbivores were more frequent in the top 5 cm soil due to the litter layer. Total nematode density ranged from 15·1 × 104/m2 (May) to 66·1 × 104/m2 (November). Monthly mean nematode biomass was 18·86 ± 8·36 mg dry wt/m2. Temperature, soil organic carbon and soil total nitrogen apparently played an important role in regulating the nematode population.