Catalytic decomposition of hydrazine over Ir/gamma-Al2O3 was investigated using catalysts with different Ir content. The catalysts were characterized by XRD, XRF, BET, and TEM. Results indicated that with increasing Ir content from 5.6 to 40.8 wt%, the BET surface area and pore volume decreased. This decrease was more significant when Ir content increased from 34.3 to 40.8 wt%. Reactor tests also indicated that the maximum stable reactor pressure of 2180 kPa with the time of about 400 milliseconds to obtain this pressure, and the lowest catalyst loss of 11.3 wt% were obtained with 34.4 wt% Ir as optimum Ir loading.