This study was designed to observe the effect of two levels of dietary protein intake on the development and growth of rats from fetus to adult. The pregnant rats were fed either 20% casein diet or 7% casein diet. After weaning or two weeks postweaning, some of the pups from malnourished mothers were rehabilitated by feeding 20% casein diet. The results were. 1. On the 14th day of gestation, no differences were found in weight and total body fat or protein between fetuses from dams fed 7% casein diet and those from those from 20% casein diet. 2. The birth weight of the pups from 7% casein diet group were significantly lower than those from 20% casein diet group. 3. After rehabilitation, the total body fat and protein of low protein group were not different from those of control group when they were compared at the same body weights regardless the age of rats or the duration on the low protein diet. 4. The nitrogen retention of low protein group, after rehabilitation, was higher than that of control group when they were compared at the same body weight.