This study was conducted to evaluate the effect of Guar Korma Meal treated with acetic acid (GKMA) on chemical composition, digestibility coefficients, milk yield, degradation kinetics, and some blood parameters of lactating cows,, Guar Korma Meal (GKM) was mixed with 3% acetic acid (v/w), followed by drying at 105oC. Treated Guar Korma Meal replaced with untreated GKM in the concentrate feed mixture (CFM) at the rate of 0, 35, 65 and 100% for the tested rations T1, T2, T3 and T4, respectively. Sixteen crossbred Friesian cows in their third or fourth lactation season were used in double 4x4 Latin squares design, whereas 4 cows fed each diet at a period of 28 days (21 as a preliminary period and 7 days as a collecting period). Three rams were consigned for digestibility trials, while other three females with rumen fistula were used for the in situ trials. The obtained results showed that increase GKMA in the experimental rations significantly (P<0.05) increased all nutrients digestibility coefficients, being the highest for T4 (100% GKMA) compared with other experimental rations. Feeding values as TDN and DCP were significantly (P<0.05) higher with increasing GKMA in the experimental rations. Both T3 and T4 (containing 65 and 100% GKMA, respectively) had the highest feeding values, being 66.16 and 66.20% for TDN and 8.10 and 8.23% for DCP, respectively. Average daily milk production as actual or 4% fat corrected milk yield, fat and protein yields, and total solids content were significantly (P<0.05) higher in T3 and T4 than in T1 and T2, being the highest in T4. Average concentration of total VFA, acetic acid and microbial-N yield in rumen liquor significantly (P<0.05) by increasing level of GKMA, being the highest for T4. Concentration of total proteins and their fractions, glucose and urea and AST and ALT activity were at the normal range. Conclusion: Conclusively, it could be recommended that can be used guar korma meal treated with acetic acid in ration formulation of dairy cows at level of 100% as a source of protein which given the best result to highest nutrients digestibility, feeding values, milk production, and feed utilization and economic efficiency.