Sea-buckthorn fruits (Hippophae rhamnoides L.) are used in Mongolia as traditional medicine due to the health-benefits associated with its bioactive components. The purpose of this study was to investigate the chemical composition of Mongolian sea-buckthorn fruits. In terms of proximate composition, crude fat content was the highest, whereas its crude ash content was the lowest. In organic acid contents, malic acid content ($6.30{pm}0.005$ mg/g) was the highest. Free sugars were composed of sucrose, xylose, glucose and mannitol. Vitamin C and carotenoid content were 320 mg/100 g and 715.25 mg/100 g, respectively. The major fatty acids were palmitic (C16:0), palmitoleic (C16:1), caprylic (C8:0) and linoleic (C18:2) acid.