Differential expression of members of the connexin (Cx) gap junction multigene family permits formation of gap junctions with the varied physiological properties required by different tissues. The aim of this study was to characterize connexin expression and the influence of all-trans-retinoic acid (RA) in mouse gingival epithelial cells (GE1). The cells were treated with RA, and expression of Cxs was analyzed by immunofluorescence, reverse transcriptase-polymerase chain reaction (RT-PCR), and real-time PCR. RT-PCR revealed that GE1 cells expressed mRNA for Cx26, Cx30.3, Cx31.1, Cx32, and Cx43. In addition, real-time PCR revealed that RA significantly decreased expression of Cx31.1 as compared with control. These results indicate that GE1 cells are useful in analyzing the expression of connexin molecules in oral keratinocytes from oral mucosal lesions.