Abstract: Sublethal concentrations of copper (CuSO4.5H2O) administered to freshwater fish, Puntius sophore for a period of 30 days brought about significant haematological alterations. RBC/TEC count, Haemoglobin, Haematocrit and MCHC content progressively decreased while WBC/TLC count, MCV and MCH increased. LC50 of CuSO4 for P.sophore was estimated as 1.6 mg/l. Alterations in haematological parameters were dose and duration dependent. The highest concentration of copper (0-8 mg/l) proved lethal and resulted in mass mortality of the fish on 15th day of the experiment.