Based on combination advantages of both supports MgO and carbon nanotubes (CNTs), a novel combination-type catalyst for ammonia synthesis has been developed, in which two catalysts, K-Ru/MgO and K-Ru/CNTs, are combined with the optimal weight ratio of 1/1. The results show that the highest catalytic activity of the combination-type ruthenium catalyst, K-Ru/CNTs+K-Ru/MgO, for ammonia synthesis reaches 4453 mu mol NH3 h(-1) g(-cat)(-1) at 673 K under 0.2 MPa, which is about two times higher than the average activity of the two catalysts under the same operating conditions. It is suggested that there is a complementary interaction between the two supports (CISS), MgO and CNTs, and the combination of both K-MgO and K-CNTs promotes electron transfer from alkali metallic atoms to the B-5-sites of ruthenium. (c) 2006 Elsevier B.V. All rights reserved.