Abstract: Kerala is the synonym to biodiversity. Fresh water ichthyological diversity is the most crucial part of biodiversity as it is difficult to be estimated and protected. The study aimed to estimate the fish diversity of Pallickal River in relation to physico chemical parameters. The period of study was from March 2012 to October 2012. Fish samples and surface water samples were collected seasonally. Specimens were preserved in 4% formalin. Identification of fishes was done with standard keys and water samples were analyzed by standard procedures. Statistical analysis of the data was done. 30 fishes belongs to 16 families of 9 orders were obtained, in which the dominant family was Cyprinidae. One endangered species and 7 vulnerable species were recorded during the study. Biodiversity indices were calculated using Biodiversity pro and the values obtained showed rich and healthy ecosystem showing less over dominance and high diversity. Dominant species differed in relation to site and season. Physico chemical parameters indicated the ecosystem as a life sustainable one, except low pH recorded at site 1 during pre monsoon period. DO, PH and TDS were identified as the principal factors those influence the piscian fauna, using PCA.