Contents In this study, sperms collected from the right and left cauda epididymis were grouped into having canine prostatic fluid (PF) sensitization or not diluted with egg yolk Tris-fructose citrate extender, and stored at 4 degrees C. The necessity of canine PF in cooled preservation was determined by elucidating the sperm quality after the storage. As a result, while there was no difference among all groups up to 48hr of storage, after storage for 96hr and more, a significantly lower sperm motility was observed in the group without being sensitized to PF than the groups with being sensitized to PF (p<.05, p<.01). Although sperm abnormality increased in all groups with increased storage time, the group without being sensitized to PF showed significantly higher sperm abnormality than did the groups with being sensitized to PF after storage for 24hr and more (p<.01). From these findings, we concluded that PF was necessary for the cooled preservation of the canine sperm because these sperms were protected from any effects of low temperatures by being sensitized to PF.