The objective of this study was to evaluate the accuracy of equation being used to estimate the total digestible nutrients (TDN) of whole crop rice silage (WCRS) in sheep. To compare the observed and estimated TDN contents [estimated TDN content=87.57-(0.737×ADF)], two varieties of WCRS from Nokyang (NS) and Samgwang (SS) as forage and food source, respectively, were used as a treatment. Nine female Corriedale sheep (average body weight: 49.2±6.3 kg) were used as the experimental animals. The ewes were fed according to their nutrient requirements at the maintenance level. To check the difference between the observed and estimated TDN contents, one sample non-parametric t-test was applied. The CP, NFE and CF contents of the NS were 43.6, 74.2 and 64.2%, respectively, and that of the SS were 46.2, 58.1 and 44.9%, respectively. The observed and estimated TDN contents of the NS were 63.5 and 61.5%, where there was no significant difference. The observed and estimated TDN contents of the SS were 48.9 and 59.0%, where there was significant difference (p<0.05) This research confirmed the validity of TDN estimation equation being used for estimation of TDN of WCRS as forage source, but further research is recommended on the equation for estimating TDN contents of WCRS as food source.