The effects of food component and concentration on the population growth, body size, and egg size of freshwater rotifer Brachionus rubens were studied using population accumulative culture method. The results showed that there were very significant effects of food component and concentration on the population growth rate, body volume and egg volume. Among three types of algal food, the population growth rate of rotifers fed with Chlorella pyrenoidosa was lowest, and that fed with Scenedesmus obliquus was the highest. Rotifers fed with C. pyrenoidosa had the smallest body volume, but there were no significant difference between the two others. The relationship between population growth rate and food concentrations was curvilinear, and it could be described as Y = -0.0040X2 + 0.0409X + 0.4471. The body and egg volumes tended to be smaller, when the food concentrations were higher than 6.0 x 10(6) cells.ml-1 and or lower than 3.0 x 10(6) cells.ml-1.