Ni-diamond composite powders with nickel layer of round-top type on the surface of synthetic diamond (140/170 mesh) were coated with semi-batch reactor by an electroless plating method (EN). The effect of nickel concentration and feeding rate of reductant, temperature, reaction time, and stirring speed on the weight percentage of deposited Ni and morphology, mean particle size, and specific surface area of the composite powders were investigated by AAS, FE-SEM, PSA and BET. The weight percentage of Ni in the composite powder increased with time and temperature but decreased with stirring speed, and the weight percentage was 55% at 150 min., 200 rpm and 70 degrees C.