This study reports haematological parameters and biochemical changes in liver, kidney, and gill after exposing rainbow trout (Oncorhynchus mykiss) to linear alkylbenzene sulfonate (LAS). Rainbow trout were exposed to LAS for a 54-day period. The three treatments included a control (unexposed), a treatment group I (0.2 mg/L LAS) and treatment group II (0.4 mg/L LAS). Below stated enzyme levels were determined at the end of the study; lactate dehydrogenase (LDH), aspartate amino transferase (AST), alanine amino transferase (ALT) and alkaline phosphatase (ALP). Enzyme activities (ALT, AST, ALP) in LAS exposed fish decreased in the liver and kidney. But LDH activities in LAS exposed fish increase in the gill. Although erythrocyte number was increased in the experimental groups, this is not statistically significant. Histopathologically observed, there wasn't any significant change in all organs of trial groups when compared to control group.