As a new carbon material, carbon nanotubes have excellent mechanical properties and special tubular structure, CNTs can be used as a reinforce body to improve the hardness and tribological performance. In this paper, Ni-P-CNTs composite coatings were successfully co-deposited by electroless plating. The optimum plating process was determined, and the effects of CNTs and heat treatment on hardness of the composite coatings were investigated. The hardness of the composite coatings was greatly improved after heat treatment. Moreover, as the increase of CNT concentration in the plating bath, the micro-hardness of the coatings was also increased.