Abstract:In Mongolia, the sea buckthorn is a nontraditional fruit crop. It has been being planted since 2000 in the Botanical garden of Medicinal plants of Monos group, Mongolia. The purpose of this study was to determine how to change biological active compounds in the Sea-buckthorn berries that depending on harvesting season and to describe which harvesting period is efficient to use. In 2013-2014, fruit samples were prepared from our botanical garden such as: Chuiskaya, Maslichnaya, Vitaminnaya, Oranjivaya, Obilniya and Red cultivars on their chemical composition depended from harvesting season. The chemical compositions of fruit were investigated from 19th August to 20th January. We determined total oil, organic acid contents, β-carotenoid, ascorbic acid, total phenolic content and polysaccharide. The chemical contents were analyzed with the Folin-Ciocalteau assay, colorimetric assay, volume metric analysis method and spectrophotometric method. During the harvesting period, the chemical compositions of samples such as total oil content and polysaccharide content were increased and the contents of organic acid, beta carotenoid and ascorbic acid were decreased. From our study, we concluded that fruit biological active compounds depend from harvest time and it could be used to choose production of seabuckthorn product types.