Sperm cryopreservation is an effective method of preserving male fertility in humans, as well as domestic and experimental animals. However, various factors such as ice crystal formation, osmotic stress, and oxidative stress, negatively influence the motility and viability of post-thawed spermatozoa. Betaine, which works as an osmoprotectant is known to work as a nontoxic cryoprotectant. However, the protective effects during mouse sperm cryopreservation are still unclear. Thus, the purpose of this study was to investigate whether betaine has protective effects during the process of mouse sperm cryopreservation. In this study, betaine was found to be effective in maintaining sperm motility during the freezing procedure and 1% (85.4 mM) betaine was identified as the optimal concentration to be added to cryopreservation solutions. It was also found that betaine improves the integrity of the plasma membranes of sperm tails, suggesting that betaine has a positive effect on sperm motility.