In this study, the effects of sea-buckthorn ( Hippophae rhamnoides L.) leaves (SL) on the biochemical parameters and metabolomic profiling in Altay lamb (Ovis aries) were observed. Sixty six-month-old male Altay lambs (body weight 28.0 ± 3.5 kg) were randomly assigned to four groups (n=15). The experimental groups were named as CON, 2.5%, 5.0% and 7.5%. The group CON, contained animals fed with a basal diet. Animals of the other groups were fed a treatment diet consisting of 2.5% (Group 2.5%), 5.0% (Group 5.0%) and 7.5% (Group 7.5%) SL. The experimental period lasted 56 days. The results showed that the average daily gain (ADG) and average daily feed intake (ADFI) increased with the increase in the levels of dietary SL. Dietary SL showed a direct relationship with total protein (TP), albumin, globulin and total cholesterol (TC) content of the experimental animals. However, an indirect relationship was observed between dietary SL and the concentration of urea nitrogen (UN). The concentrations of glucose, high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) showed quadratic change. Additional changes occurred in the endogenous metabolites involving multiple pathways. The pathways were tricarboxylic acid (TCA) cycle, the metabolism of protein and amino acid and the metabolism of fatty acid and steroid. The changes in metabolites primarily revealed an increase in amino acids and carbohydrates and a decrease in lipid metabolites. These findings provide a comprehensive insight into the effects of the metabolic aspects of sea-buckthorn leaves on Altay lambs. In addition, the present research results provide a better understanding to the development and utilization of sea-buckthorn as a healthy additive for small ruminant production. Keywords: Hippophae rhamnoides L., lamb, metabolomics, growth performance, serum parameters