Sugars are the principal carbon and energy sources involved in the signal transduction and stress resistance mechanisms of plants. Their roles are closely linked to their transport across cell membranes in plants. Transmembrane sugar transport is mediated by three sugar transporters: sucrose transporters, monosaccharide transporters, and sugars will eventually be exported transporters (SWEETs). SWEETs have been shown to play vital roles in many physiological processes in herbaceous angiosperms. However, existing information on the sugar transporters of trees, especially conifers (gymnosperms), is limited. Therefore, elucidation of the functions and physiological roles of sugar transporters is necessary to better understand the tree growth and development processes. In this study, we isolated the SWEET gene (cDNA), CjSWEET1, from Cryptomeria japonica (sugi), an important forestry conifer species of Japan. Sequence analysis revealed that the CjSWEET1 cDNA-encoded protein had seven transmembrane domains, with the N- and C-termini located outside and inside the membrane, respectively, consistent with previously reported SWEETs. To assess the monosaccharide uptake of CjSWEET1, complementation tests were conducted using a hexose uptake activity-lacking yeast strain (Saccharomyces cerevisiae). The CjSWEET1-transformed yeast strain grew in the medium containing glucose as the sole sugar source. This indicates that the heterologous expression of CjSWEET1 overcame the deficiency in this strain, suggesting its important role in glucose uptake. Expression analysis revealed that CjSWEET1 was expressed in all parts of the sugi tree, including the male strobili and seeds. These results highlight the role of CjSWEET1 in the transmembrane glucose transport of sugi trees.