The thymus weight of the mouse was 54.1% in protein malnutritive diet group and 39.2% in group treated with saponin fraction of Panax ginseng in comparison to normal diet group. This decreasing effects of protein malnutritive diet and saponin fraction on the thymus weight practically disappeared after four weeks. The saponin fraction showed no effect on the spleen weight of the mouse. The supplement of the saponin fraction enhanced total peritoneal exudate cells, content of total serum protein and albumin content of the mouse, each 45, 8 and 10% respectively in comparision to that of normal diet group. And these values in protein malnutritive diet group were 61.2, 83.6 and 87.0% respectively in comparision to that of normal diet group, and recovered to the level of normal diet group by the supplement of the saponin fraction. The electrophoregram of the serum protein of the mouse fed with protein malnutritive diet was different from that of the mouse fed with normal diet, but this difference practically disappeared by the supplement of the saponin fraction.