Demographic structure and vertical distribution pattern of a curly wood louse, Cylisticus convexus in three study areas (Mekkarai, Kottavasal and Achankovil) in different seasons were studied, with special reference to soil edaphic and chemical factors. The density of wood louse was low during summer season (9.75± 2.5 &12.3± 4.6), moderate in monsoon season(36± 8.28 & 18± 3.2) and very high during post monsoon season(36.4± 6.2 &19± 3.36). The population density of Cylisticus convexus was high in Achankovil area in all seasons when compared to Mekkarai and Kottavasal except in summer, during which the population density was almost same in all the three study areas. Soil of Achankovil has high organic carbon (2.45%) and magnesium (79ppm) and calcium content (1754ppm). Soil of Mekkarai has high amount of nitrogen (2511ppm) and phosphorus (3.9ppm). The vertical distribution of Cylisticus convexus in soil is very low.It goes to a maximum depth of 30cm only from the surface. The Population density of this isopod is very high in the top soil than the middle layer even in summer. The distribution patterns of Cylisticus convexus mainly depends on the availability of high organic carbon content and low phosphorus and nitrogen content in the soil, which could substantiate their rich density in Achankovil than Mekkarai and Kottavasal.