This study was based on the monthly collections of the wood boring isopod, Sphaeroma terebrans from Ayiramthengu, Karunagapally and Neendakara and S. armandalei from Aroor taken during the period 1965-66. Five species of ciliates namely Lagenophrys cochinemis, Folliculin sp., Zoothamniumrigidum, Cothurnia gammari, Vorticella campanula ; the ostracod Microsyssitria indica and the isopod lais singaporensis were found to be associated with these wood boring isopods. The seasonal incidence and relative abundance of the associated organisms of these isopods in relation to hydrographical conditions were studied. Among these associated organisms, L. cochinensis was the most abundant of all the species. The data were statistically analysed and it was found that their occurrence Is significantly different during different months of the year. In general, the number of organisms and the species were found to be associated more with S. terebrans than with S. cmnandalei.