Microfauna in the flood water, the oxidized layer, and the reduced layer, of a submerged paddy soil was examined to study the adaptation, survival, and multiplication of animals in these habitats. The microfauna was extracted for 48 h (the first 24 h and the succeeding 24 h) from the soil by the Baermann method. It was assumed that the first and the succeeding extractions yielded active and dormant animals, respectively. In the flood water, relatively large and mobile animals predominated. On the contrary, in the reduced layer, active animals were small in size and tolerant to the reduced state and the remaining ones took dormant forms. These dormant animals woke up when the soil was oxidized. This survival strategy of the soil microfauna was found to be effective to cope with reduced soils and toxic chemicals such as BHC. Microfauna in the oxidized layer was more complex than in the other two habitats, presumably because the oxidized layer provided various microsites to the fauna.