This experiment was made in order to clarify the difference in growth rate for rats between the purified whole egg protein and lactalbumin. It was shown that body weight gain was 7.0 and 5.9g/day, and protein efficiency ratio (PER) was 4.2 and 3.8, for the whole egg protein and lactalbumin, respectively. It was concluded that the purified whole egg protein is preferable to be taken as the reference protein for assay purposes in the rat.