Abstract: Population density, diversity, and species association of soil groups in general and species association of a soil isopod Phyloscia javanensis in particular was studied. The monsoon season has maximum soil animal group density followed by post monsoon and summer. The vertical migration and thermal sensitivity of most of the soil animals contributes to the decrease of population density of most of the groups in summer in both ecosystems. The species under special study showed maximum association in monsoon in both ecosystems and least during summer. This species has low association ability when compared with others micro-arthropod groups. This is because the soft bodied animal often happens to be the prey of many of the soil macro arthropods and Gastropods. So they always go to the seat of safety in the crevices of pebbles and stones. So their density will be always low in the collecting samples.