The NiNaY composites have been investigated using various techniques to explore their hydrogen adsorption performance and structural characteristics. Hydrogen adsorption capacities of reduced NiNaY composites were significantly enhanced under various temperatures and pressures. Most noteworthy is that at room temperature and low pressure, hydrogen adsorption amount was increased by a remarkable factor of 7.1 for reduced 10 wt% NiNaY composite. Dissociative hydrogen adsorption and subsequent hydrogen spillover at high pressure have enhanced hydrogen adsorption capacity by a factor of 0.4 and 0.86 on reduced 10 wt% NiNaY composite at 77 and 303 K, respectively. The enhancement effect of hydrogen adsorption on the reduced composites at room temperature is determined by hydrogen adsorption on available nickel sites which were characterized by the active nickel surface areas. However, the optimized hydrogen adsorption enhancement effect on the composite at 77K is achieved by a combination of suitable active nickel surface area and active support area. The results suggest that spillover effect is occurring at 77K on the reduced NiNaY composites. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.