Composite particles prepared by spray pyrolysis of aqueous solution of AgNO3 and Ni(NO3)2·6H2O with 10 vol%H2-N2 were characterized and compared with the particles similarly prepared from their pure nitrates. The composite particles were composed of metallic silver, nickel oxide or metallic nickel, depending on the condition, with no trace of alloy. The existence of nickel ions dispersed throughout the particles did not affect the rate of reduction to the highly reducible silver but retarded its subsequent crystal growth. On the other hand, both the reduction to nickel and its crystal growth were all retarded due to the existence of the more reducible silver ions. In addition to these, the incompatibility also increased the size of the composite particles from the corresponding single component particles and kept it almost constant with respect to the preparation temperature.