In this paper, the effective thermal conductivity (ETC) of sintered metal powders used in loop heat pipe wicks has been investigated. Experimental tests were performed on wicks sintered from pure nickel powder and nickel-copper powder mixtures in both dry mode and wet mode. Results show that ETC of sintered Ni-Cu wicks was less than that of sintered pure nickel wicks; ETC of sintered Ni-20 wt% Cu wicks decreases significantly, with a factor of 2.4 in dry mode and 2.2 in wet mode. The results of experiments are presented and analyzed with help of X-ray diffraction. (C) 2010 Elsevier Ltd. All rights reserved.