In the current study, tyrosine aminotransferase (TAT) as a target enzyme was purified from the liver of control and Schistosoma-infected mice that was subjected to catalytic investigation. The purified enzyme has a single band on SDS-PAGE with a molecular mass of almost 100 KD from control and infected mice. The kinetic studies of hepatic TAT towards its substrates showed no change in Km, whereas Vmax value was increased from 2.3 to 2.9 fold in the enzyme isolated from Schistsoma- infected mice. In addition, the Kcat/ Km ratio displayed a higher value for the enzyme from infected mice, indicating that it is more efficient and specific. On the other hand, the in vitro effect of praziquantel showed a slight activation of hepatic TAT in both control and infected mice, whereas mirazid (MZD) has an inhibitory effect in a concentration-dependent manner. The response of TAT from infected mice towards MZD inhibition is less than that from controls. These data suggest that there is a change in the catalytic properties of hepatic TAT in schistosomiasis and the in vitro effect of the schistosomicidal drugs appears to have inductive or inhibitory effect.