This study examined the effect of three forms of co-ensiled rice straw (RS) with whole sugar beets (SB) crushed on milk production and constituents of lactating cows. The first type (S1) incorporated immersed corn grains (CG) for 24 h (81.96 kg CG per ton, RS), while the 2^nd and 3^rd forms (S2 and S2) contained SB instead of 50 and 100% of CG on an energy basis, respectively. Experimental silages were offered ad libitum separately with a concentrate feed mixture on one of the experimental diets, D1, D2, and D3, respectively. The silage S3 had non-significant (P> 0.05) population of lactic acid bacteria, yeasts and aerobic bacteria compared to other silages. The DM, OM, CP, EE, NFC, and TCH contents of S1 were slightly (P> 0.05) higher than those of S2 and S3, while the opposite was happened with the NDF and ADF contents. The digestibility of CP and EE in all dietary groups did not differ. However, the digestibility of OM, NDF and ADF in the D3 was higher (P< 0.05) than in D1 and D2. Moreover, the D3 group recorded the highest values (P< 0.05) of silage consumption and palatability, while the lowest values for silage refusal were recorded compared to the D1. Milk production, fat corrected milk (FCM), and energy corrected milk (ECM) were (P< 0.05) higher for cows fed D3 compared with D1 and D2. Protein, lactose, and total solids, as well as solids not fat (%), were higher (P<0.05) for D3 than for the other diets except fat% was higher than fed D1. The feed conversion ratio (FCR) of cows fed diet D3 was better than that of cows fed D1 and D2 diets. Blood constituents remained unchanged and were within normal ranges. In conclusion, co-ensiling RS with the whole SB plant is considered a good method to improve its nutritional value and the performance of dairy cows