The diversity of insect fauna of Vellayani lake in Kerala was represented by 60 species classified under 37 families and 8 orders. Among the entomofauna collected from the lake, the order Coleoptera was diverse in number of genera (22). Shannon index was highest in station 2 (3.214) and lowest (2.839) in station 4. The higher richness index was also recorded in station 2 (6.331), though the lowest species richness was observed in Station 1 (5.205). The order Ephemeroptera is represented in Vellayani lake by the families Baetidae and Caenidae, which are considered as an indicator of water quality. Of the 15 metrices selected, taxa richness, Composition measures, Tolerance and Intolerance and Functional groups were also found out for all the stations. In the present study, the percentage of Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa richness and diversity remained high in Station 1, 2 and 3 but reduced drastically in stations 4 and 5. The high HBI value recorded at station 4 is due to the abundance of pollution tolerant taxa such as Chironomidae, Tabanidae, Culicidae and Anophilinae. The results of the study reveal greater diversity of aquatic entomofauna in Vellayani freshwater lake and suggest the possibility of using insects effectively for biomonitoring programmes.