Abstract: Objective: This study was carried out to investigate inoculating sugar beet leaves silage with lactic acid bacteria to reduce negative effect of its content of oxalates. Materials and Methods: Fifteen lactating Frisian cows weighed 500 ±30 kg were randomly assigned into three groups (5 cows) using complete random design. The experimental diets were as follow: T1 group was fed 50% (Concentrate Feed Mixture, CFM); 30% corn silage and 20% rice straw, T2 group was fed 50% (CFM); 30% untreated sugar beet leaves silage and 20% rice straw and T3 group was fed 50% (CFM); 30% treated sugar beet leaves silage and 20% rice straw. Dry matter intake and milk yield were recorded and the samples of blood plasma, rumen liquor, milk and feed were analyzed and the data were statistically analyzed according to a completely randomized design using GLM procedure of SAS program. Results: The results showed that treated silage with lactic acid bacteria was higher in calcium, lactic acid and acetic acid contents but lower in values of pH, oxalate, cellulose, hemicellulose and butyric acid compared with untreated silage. Roughage DMI decreased with cows fed T2 compared with other groups. Also, nutrients digestibility and nutritive value were decreased in T2 compared with the T1 and T2. However, ruminal TVFA's, acetate acid, CH4 production and blood glucose decreased significantly (p<0.05) in T2 compared with other groups. T2 recorded the lowest values (p<0.05) for milk yield and energy corrected milk compared with other groups, milk compositions of cows were affected with treatments. Conclusion: It is concluded that ensiling sugar beet leaves treated with lactic acid bacteria reduce oxalate contents in sugar beet leaves silage and enhance performance and productivity of lactating Frisian cows.