A cDNA of aquaporin (AQP, water channel) belonging to the major intrinsic protein (MIP) family was obtained from the digestive tract of the Formosan subterranean termite, Coptotermes formosanus. The cDNA encoded an AQP homolog designated as CfAQP with 249 amino acids. RT-PCR analysis revealed the expression of CfAQP in the digestive tract and other tissues, suggesting that CfAQP may play important roles not only in water recycling but also other essential water transport processes in the termite. Phylogenetic analysis of CfAQP with 71 insect MIP sequences from 17 species indicated that insect MIPs could be classified into 4 groups, designated as insect MIP Group 1 to Group 4, and that CfAQP is a member of Group 1, a sister group of vertebrate AQPs.