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Floral scent is a key ornamental trait that determines the quality and commercial value of orchids. Geraniol, an important volatile monoterpene in orchids that attracts pollinators, is also involved in responses to stresses but the geraniol synthase (GES) responsible for its synthesis in the medicinal orchid <i>Dendrobium officinale</i> has not yet been identified. In this study, three potential geraniol synthases were mined from the <i>D. officinale</i> genome. DoGES1, which was localized in chloroplasts, was characterized as a geraniol synthase. <i>DoGES1</i> was highly expressed in flowers, especially in petals. <i>DoGES1</i> transcript levels were high in the budding stage of <i>D. officinale</i> flowers at 11:00 a.m. DoGES1 catalyzed geraniol in vitro, and transient expression of <i>DoGES1</i> in <i>Nicotiana benthamiana</i> leaves resulted in the accumulation of geraniol in vivo. These findings on DoGES1 advance our understanding of geraniol biosynthesis in orchids, and lay the basis for genetic modification of floral scent in <i>D. officinale</i> or in other ornamental orchids.