In this study effects of secondary cooling rate upon morphology and size of primary particles in Al-7.1wt% Si slurry produced by SSR process were examined. SSR slurries with various solid fractions were poured into a wedge-shaped steel die to produce a range of secondary cooling rates. The extent of primary particle growth during secondary cooling at various cooling rates was estimated at 0.05, 0.1, 0.2, 0.3 solid fractions using a 1/3-power law relationship. The results indicate that for a given cooling rate primary particles in higher solid fraction SSR slurries grow less significantly during quench than those in low solid fraction slurries. The shape factor of primary particles also depends on secondary cooling rate and solid fraction and decreases with increasing the secondary cooling rate and/or the solid fraction.