The effect of temperature, dose-rate and various additives such as acetone, nitrate ion, nitrous oxide and water have been studied in γ-radiolysis of liquid ammonia. Up to doses of about 1019eV/g almost dose-independent G-values of 0.12 for N2H4, 0.82 for H2 and 0.21 for N2 were obtained at 30°C.The N2H4 concentration at the steady-state was 5.6 × 10-7 mol/NH3 mol for doses greater than 8 × 1019eV/g, where G-values of H2 and N2 increased to 0.84 and 0.27, respectively. The stationary N2H4 concentration showed a significant increase upon lowering the irradiation temperature in the case of liquid phase. In solid phase, at -196°C, G-values were 0.08, 0.2 and 0.04 for N2H4, H2 and N2, respectively.The rate of formation of N2H4 depended on dose-rate at relatively high dose. The presence of nitrous oxide, a typical electron scavenger in aqueous solutions, led to a decrease in the N2H4-yield. On the other hand, a maximum yield of N2H4 was obtained at the concentration of about 50 mol % NH3 in an aqueous solution at the irradiation temperature of 30°C.