Abstract: In the present study, a series of five members heterocyclic where synthesized by the reaction between isoniazid and various substituted isothiocyanates. The newly synthesized compounds where characterized by IR and 1H-NMR spectral data. The effect of Thiadiazole derivative (2b) in monocyte and lymphocyte in the differential count is 20349 and 11415 cells cu.mm^-1, respectively. Prepared compounds (2a and b) where not effective against differential count of eosinophil. In WBCs differential count that significant immune effects were occurring in compound (2b) more than in compound (2a). Liver enzymes, Glutamic Oxaloacetic acid Transaminase (GOT) and Glutamic Pyruvic acid Transaminase (GPT) were chosen to assess liver function. In comparison with control, the administration of Thiadiazole derivatives (2a and b) significantly declined the activity of GOT, GPT and Urea. These results indicate that prepared compound effectively increases of immune system in the animals.