The levels of arginase in erythrocyte and liver in sheep with fasciolasis and some biochemical properties of arginase in liver tissue were investigated. This study was carried out using 120 sample of blood and liver. Tiyosemicarbazide-Diasetilmonoxim-Urea method was used to measure arginase activity. There was no difference between groups with fasciolasis and control groups for activity of erythrocyte arginase (P>0.05). The levels of arginase activity in liver decreased significantly in the group with fasciolasis when compared with control group (p<0.01). There was no difference between healthy sheep and sheep with fasciolasis for biochemical properties of liver arginase enzyme. It was determined that presence of 1 mM Mn⁺² ions, 15-minute-preincubation at 65ºC and 10 minute-incubation at 37ºC are necessary for activation of arginase in liver tissue of sheep. The most suitable buffer for enzyme of arginase in liver tissue is bicarbonate buffer and it was found about optimal pH: 10. Km which is against L-arginine-substrat of enzyme-was found by the method of Michaelis-Menten and Lineweaver-Burk and it is about 4 mM.