The research includes the study of some protease properties in seven patients diagnosed with kidney tumors. Three of them were benign and the others were malignant. The samples were collected from the patients directly after undergoing the surgery in Al-Jamhoory hospital in Nineveh Governorate, Iraq. Protease enzyme was isolated using different biochemical techniques, like ammonium sulphate precipitation, dialysis and gel filtration chromatography on sephadex G-100. The comparative molecular weight of protease was determined using gel filtration and was found to be (72000 and 75000 ± 2000) dalton for benign and malignant tumors respectively. The results showed that there was a (55%) increase in the specific activity of protease in malignant kidney tumors than benign. The optimum conditions for protease activity were obtained using sodium borate buffer at pH (8.8) for (1) minute incubation at (40°C) and (0.4) mM of casein as a substrate V max and K m were found to be (0.87 U/ml) and (0.22 mM) respectively by Linweaver-Burk plot. Finally, the effect of some chemical compounds like iodoacetamide, mercurous chloride, zinc sulphate showed an inhibition impact on protease activity while calcium sulphate and magnesium chloride demonstrated an increase effect on the protease activity.