Fluorescein diacetate hydrolyzing activity (FDHA) of soils, both in field moist and air dried, of different agro-ecosystems in alluvial soil was studied. Field moist soils recorded higher values than in air-dried soils, but they showed significant positive correlation (0.93**). FDHA in both soil pretreatments showed positive correlation with organic matter (0.98** for field moist soil and 0.92** for air-dried soil) and clay content (0.85** for field moist soil and 0.82* for air-dried soil) of the soils. Multiple regression analysis showed that the stabilization of FDHA in the studied soils was due to organic matter-enzyme complex. Among the organic matter fractions, humus C plays dominating role to control the FDHA of the soils. © 2006 Taylor & Francis.