The permeability of water and cryoprotectants through the plasma membrane is very important for cryopreservation of mammalian cells. Aquaporin 1 (AQP1) is one of the water channel proteins localized on the membranes of various cells including reproductive organs, allowing water to flow rapidly across the plasma membranes in the direction of osmotic gradients. Although mRNA expression of AQP1 was reported in the mammalian testis by reverse transcription polymerase chain reaction (RT-PCR), protein and mRNA expressions of AQP1 have not been confirmed to date in the sperm of any species. The present study was conducted to determine whether AQP1 mRNA is expressed and AQP1 protein exists in canine spermatozoa. Results from RT-PCR showed that AQP1 mRNA was expressed in canine spermatozoa as well as the testis. The size was similar to the one from canine genomic DNA as a positive control. In sperm, AQP1 protein was also detected by canine AQP1 specific antibody. From these results, both AQP1 mRNA and protein are expressed in male gamete in the dog. Expression of AQP1 may be involved in the flux of water during the cryopreservation of spermatozoa.