Urease activity (by buffer and non-buffer method) of soils of different agro-ecosystems in alluvial soil was studied. Urease activity by buffer method records a higher value than the non-buffer method. Both the methods showed significant positive correlation (0.99**) between each other. Urease activity by both methods showed positive correlation with organic matter (0.88** and 0.89**, buffer method) and clay content (0.91** and 0.83*, non-buffer method)) of the soils. Multiple regression analysis showed that the stabilization of urease activity in the soils studied was due to an organic matter-enzyme complex. Among the organic matter humus C plays a dominating role to control the urease activity of the soils. © 2004 Taylor & Francis Ltd.