Abstract : In the study was based on studying the cytotoxic effect of arginase enzyme on breast cancer cell line (MCF-7), the purified arginase was showed highest inhibition for growth of breast cancer cell line (MCF7) with an IC50 of (116.0) μg/ml in comparison with an IC50 of (136.4)μg/ml for normal cell line. Five concentrations (200, 100, 50, 25, and (12.5) μg/ml of purified enzyme arginase was tested on breast cancer cell line (MCF-7) to detect the changes in six cellular parameters using high content screening system (HCS) (viable cell count VCC, nuclear intensity NI, cell membrane permeability CMP, mitochondrial membrane potential MMP and cytochrome C) reading result revealed that the concentration (200 μg/ml) have highest significant effect on the most parameters when compared with control.