This study was carried out between November 2007 and October 2008 in the experimental farm of Chunnam National University to investigate the effect of feeding of whole crop barley silage on the reproductive performance of Hanwoo heifers and cows. Two diets, rice straw or whole crop barley silage separately from concentrate were fed 11 Hanwoo heifers and 26 Hanwoo cows. In control group (=CON), heifers (n=6) and cows (n=13) were fed 7 kg (/head) rice straw and 4 kg (/head) commercial diet. In whole crop barley silage group (=WBG), heifers (n=5) and cows (n=13) were fed 8 kg (/head) whole crop barley silage and 1 kg (/head) commercial diet. 1. Conception rates for first service in CON or WBG heifers were 66.7% (4/6) and 60.0% (3/5), respectively, and the services per conception cows were $1.5{pm}0.2$ for CON and $1.4{pm}0.2$ for WBG group. 2. Days to post-partum insemination were $106.6{pm}26.3$ days for CON and $85.6{pm}12.6$ days for WBG group, and days to post-partum conception in CON or WBG were $128.4{pm}27.1$ and $96.8{pm}16.8$ days, respectively. 3. Post-partum conception rates for first service in CON or WBG were 76.9% (10/13) and 84.6% (11/13), respectively, and caving interval was $418{pm}50.7$ days for CON and $392.8{pm}20.7$ days for WBG group.