Sm2Co17 particles, with several hundreds of nanometers to a few micrometers in diameter, were synthesized by a combination of salt-assisted ultrasonic spray pyrolysis and a reduction-diffusion (R-D) process. It was found that NaCl plays a decisive role toward the suppression of particle coalescence during R-D process. By optimizing a reductant contents, the single-phased and non-agglomerated Sm2Co17 particles were obtained. In addition, particle size was controlled by varying calcination temperature from 800 degrees C to 1100 degrees C and size-dependent magnetic properties were observed. The optimum magnetic properties were achieved at a calcination temperature of 900 degrees C: coercivity of 5.3 kOe, a saturation magnetization of 99.33 emu/g, and a remanence of 56.53 emu/g.