To investigate the availability of hamster test in assaying the fertilizing capacity of dog sperm and the effect of canine sperm motility on sperm binding and penetration, semen were collected from four dogs(three dogs had been proven to be fertile and one dog to be subfertile during the past two years) and then preserved in BWW(Biggers, Whitten, Whittingham) medium for about 20 hours. The semen were given each different treatment according to the experimental design and coincubated with zona-free hamster ova for 5 hours. The ova were stained by lacmoid and examined under phase contrast microscope to investigate the rates of ova bound with sperm(sperm binding) and ova penetrated by sperm(penetration), and also numbers of both bound and penetrated sperm per ovum. In comparison between fertile dogs and a subfertile dog, the rate of sperm binding was higher in fertile dogs than the subfertile dog(p<0.01, p<0.05). The number of bound sperm per ovum was considerably higher in a fertile dog than the subfertile dog((p<0.01), and also difference of number of the bound sperm was obtained among the fertile dogs(p<0.01, p<0.05). The rate of penetration as well as the number of penetrated sperm per ovum was higher in the fertile dogs than the subfertile dog(p<0.01, p<0.05). In fertile dogs. the canine semen preserved at 4$^{circ}C$ for 18 to 22 hours showed from 30 to 80% motility at Insemination, however, no difference in hamster test was obtained according to different degree of sperm motility. These results indicated that hamster test would be of avail in assaying the fertilizing capacity of dog sperm.