The density of W-(10, 20)% Cu alloy sintered in hydrogen was in detail studied in relation to the manufacturing conditions such as ball-milling time, sintering temperaturs, etc. The sintered density did not easily reach the theoretical values, because heterogeneous microstructure appeared generally, caused by the starting mixed powder containing a small number of elongated copper rich flaky particles formed during ball-milling. The heterogeneous structure was accompanied by the micro-pores formation around the periphery of the flaky particles.