A HTP (High Test Peroxide) microthruster for maneuvering the attitude of small satellites is developed. The problems of miniaturization are investigated, the design concept of a 100mN HTP microthruster is proposed and the microthruster is demonstrated to perform a minimum impulse bit of 10 -2 N-s, which can provide slew at a speed of 0.1°/s for a micro-satellite. The total volume of the microthruster prototype is about 0.9cm3 with a throat diameter 0.5mm. Packed Silver flakes are used as catalyst, and 92% hydrogen peroxide is adopted with a flow rate 0.18g/s. Measurements of the ignition delay at different catalyst bed preheating temperatures are compared to define the operating parameters for practical applications. To improve the decomposition, the effect of pH value on HTP microthruster performance is also investigated. Test results show that the HTP microthruster gives a fine C* efficiency and a short ignition delay comparable to large scale systems in performance. Performance tests at sea-level, the developed microthruster can produce 182mN with a specific impulse 101s.