Chitosan supported palladium nanoparticles (Pd NPs/CS) catalysts were facilely prepared via an in-situ reduction of PdCl2 method and characterized by various techniques. The results showed that the palladium particles were in the range of 4–8 nm and evenly dispersed on chitosan. Furthermore, the resulting Pd NPs/CS catalysts showed high catalytic activity for the hydrolytic dehydrogenation of ammonia borane (NH3BH3, AB) in aqueous solution. As for the catalytic reaction with an activation energy (Ea) of 36.25 kJ mol−1, the orders of palladium and AB concentrations were 0.81 and 0.45, respectively. The maximum turnover frequency was as high as 24.76 molH2·molPd-1·min-1 at 30 °C. In addition, the Pd NPs/CS catalysts still kept satisfied catalytic activity even after eleven runs.