Juvenile Sydney rock oysters (Saccostrea commercialis) were fed diets composed of either one of twelve algal species or one of eleven algal species in combination with Skeletonema costatum. When used as the sole diet for 21 days, the diatoms Skeletonema costatum, Chaetoceros calcitrans. Chaetoceros gracilis and Thalassiosira pseudonana produced the greatest live weight increase in spat. When Skeletonema costatum was fed in combination with the remaining eleven algal species for 19 days, diets including Chaetoceros gracilis, Tetraselmis chui and Tetraselmis suecica produced the highest live weight increases. These findings indicated differences in the food value of several algal species to larvae and spat of the Sydney rock oyster.