This work was fulfilled to assess the effect of supplementation diets with thyme plant in buffalo calves on growth performance criteria, digestibility coefficient and certain biochemical indices. A total number of 15 buffalo calves of (4-6) months of age and 121.44 kg average body weight were classified randomly into three equal groups (5 animals per each): Animals of T1 (control group) were fed on basal diet only and those of T2 and T3 (treated groups) were fed basal diet supplemented with 5 and 10 g of thyme plant per head daily, respectively. The experiment was expanded for 90 days. Blood plasma was obtained from all experimental animals in all groups at the finishing of study for detecting certain blood biochemical parameters. Results showed that treated groups were higher (P≤0.05) in blood plasma total protein, albumin and triglyceride, globulin (P≥0.05), while there were non-significant decreases in BUN (Blood urea nitrogen), AST, ALT and creatinine levels in treated groups with thyme (T2 and T3) in comparing with those in control one (T1). Groups supplemented by thyme plant (T2 and T3) recorded improvement (P≤0.05) in digestibility, growth performance and best feed conversion ratio compared with the control group (T1). The results collected from this study proposed that buffalo calves fed diets supplemented with thyme plant as a medicinal herb, showed significantly higher total weight gains, daily weight gains, and feed conversion rates.