In this study, ultrafine nickel particles (UFPs) were produced using an Ar-9.6%H₂ RF plasma by feeding the raw powder of 10μm diameter. The effect of powder feeding rate on the yield and the specific surface area of UFPs was investigated by varying the powder feeding rate in two orders of magnitude (0.07-7.19g/min). The composition and flow rate of plasma gas, the power of plasma and the internal pressure of apparatus were kept constant during the experiments. Furthermore, the applicable range of Brownian coagulation mechanism was discussed. The UFPs were isolated and spherical in shape when the powder feeding rate was low; while they were collided and coalesced particles when the powder feeding rate was high. The specific surface area of UFPs was the highest at a low feeding rate, although it was not dependent on the collection sites when the powder feeding rate was higher than 0.2g/min. The present experiments suggested that the particle formation is controlled by Brownian coagulation in a narrow range of powder feeding rate at a relatively low value.