The performance of several catalysts to decompose the high test peroxide (HTP) was described in this paper. Manganese oxide, Platinum and Iridium were coated on the gamma alumina. The catalyst activity as active materials was measured at the flask reactor. The response time of various catalysts was also measured with a 50 Newton class thruster. Ir/Al2O3 that showed the best activity in the flask reactor and response time at the thruster, failed the reaction when continuous mode test was carried out with the thruster. Pt/Al2O3 and MnO2/Al2O3 can be substitutes to decompose the HTP. In addition, for larger thruster, MnO2/Al2O3 can be a good catalyst because its cost is below 5 % of Pt/Al2O3.