Fingerlings of Labeo rohita were exposed to acute toxic dose (12.5 ppm) of unionized ammonia for analyzing changes in biochemical parameters viz. total serum proteins, glucose, blood urea content and also to evaluate response of various enzymes like ALP, LDH, AChE, AST and ALT during exposure to 96 hr. acute toxicity assay. The serum protein content exhibited a decreasing trend in exposed fishes in contrary to glucose and urea levels which showed gradual increase in exposed fishes when compared to control fish. A similar trend was also noticed in serum enzyme responses of exposed groups, when compared to control fish. Enzymes like AST, ALT, LDH and AChE exhibited enhanced response in exposed group of L. rohita fingerlings at all intervals over control fish, except ALP which showed a decreasing trend.