Biological value (BV), net protein utilization (NPU) and protein efficiency ratio (PER) of the β-casein fraction (βCN; 65% β-casein) were compared with those of whole casein (WCN; 30% β-casein) in rats. The BV of rats fed βCN (87.2±0.6) was significantly higher than that of rats fed WCN (82.6±0.7). The NPU of rats fed βCN (87.0±0.7) was also significantly higher than that of rats fed WCN (82.3±0.7). In the PER test, βCN provided slightly greater weight gain for rats (130±6) compared with WCN (121±5). The PER of rats fed βCN (3.51±0.08) was also slightly higher than that of rats fed WCN (3.33±0.10). The data presented here suggest that the nutritive value of βCN is higher than that of WCN.