In the present study, an attempt has been made to analyze the changes in the biochemical parameters in the brain tissue of Catla catla for 21 days. The sublethal concentration of arsenic alters such as total protein, amino acid, glycogen, glucose acetylcholine and acetyl cholinesterase in the brain tissue. Protein, glycogen and acetyl cholinesterase were decreased .Amino acid, glucose, and acetylcholine were increased in the brain tissue due to toxicity of arsenic.