This experiment was conducted to find the effective use of whole crop silage of rice plant (WCSRP) by examining the feeding value of WCSRP with different relative amount of concentrate and urea supplement. Six experimental plots were set up ; i. e., 10 : 0, 6.5 : 3.5 and 7 : 3 proportions of WCSRP and calf-feeding concentrate on dry matter basis with or without supplement of 2% urea per dry weight. All mixed rations were fed freely. The trials of digestion and nitrogen retention were designed using two 3×3 Latin square methods. Dry matter intake was greater in higher proportion of concentrate ration but did not affect with urea supplement. There was no significant difference in the digestibilities of dry matter and NDF among treatments. An apparent digestibility of crude protein was relatively higher by urea supplement, particularly in WCSRP feeding alone, where a remarkable effect of urea supplement was observed. Nitrogen retention was greater in higher concentrate feeding, but little effect of urea supplement was observed in all ratios of WCSRP and concentrate. The effect of urea supplement on improving nutritive value was not clear in all combine feedings of WCSRP and concentrate. Acetic acid concentration (mol%) in rumen liquor was reduced by urea supplement in WCSRP feeding alone. Concentrations of ammonium-N in rumen liquor and urea-N in blood plasma increased remarkably by urea supplement.