Haematological measures are frequently employed as stress indicators in fish and to evaluate their overall health. This study evaluated the sublethal effects of the organophosphate insecticide chlorpyriphos on a number of haematological parameters in freshwater fish, specifically Anabas testudineus. Based on comparisons between control and experimental groups exposed to sublethal amounts of chlorpyrifos (0.125 and 0.250) at 7, 14, and 21 days, the effect was evaluated. Red blood cell counts, haemoglobin levels, WBC, and thrombocyte counts were found to decline as chlorpyrifos concentrations and days increased. White blood cell counts rose on the seventh day of exposure but fell on the fourteenth and twenty-first days when chlorpyrifos concentrations rose. According to the study, chlorpyrifos had a major negative effect on the fish's health, and haematological measures might be used as a diagnostic tool to determine whether A. testudineus has been exposed to chlorpyrifos.. KEYWORDS :A. testudineus, Chlorpyrifos, haemoglobin, Rbc, Wbc, haematological.