Coconut (Cocos nucifera L.) is one of the most characteristic plants of tropical areas. Coconut oil and its derivatives have been widely used in various industries. In this paper, a type 2 diacylglycerol acyltransferase (DGAT2), which is one of the key enzymes involved in triacylglycerol (TAG) biosynthesis, was first characterized in coconut pulp (endosperm). The results indicated that CoDGAT2 was highly expressed in coconut pulp approximately 7 months after pollination. The heterologous expression of CoDGAT2 in the mutant yeast H1246 restored TAG biosynthesis in the yeast, which exhibited substrate preference for two unsaturated fatty acids (UFAs), palmitoleic acid (C16:1) and oleic acid (C18:1). Moreover, the seed-specific overexpression of CoDGAT2 in Arabidopsis thaliana led to a significant increase in the linoleic acid (C18:2) content (approximately 6%) compared with that in the wild type. In contrast, the proportions of eicosadienoic acid (C20:1) and arachidic acid (C20:0) were decreased. These results offer new insights on the function of CoDGAT2 in coconut and provide a novel molecular target for lipid genetic modification to change the fatty acid (FA) composition of oils.