Aromatase is an enzyme that converts testosterone to estrogen. This enzyme, present in the sperm as well as various tissue and cells, has been considered to be related to the fertility of human and mouse sperm. Therefore, we examined effect of aromatase inhibitor on viability and fertility of sperm, and quantity of aromatase in sperm groups with different density in pig. To analyze the effect of aromatase on sperm viability, we treated aromatase inhibitor to the sperm with different concentrations (0, 10, 20, 50, 100, 200, 500 μM) at different time (0.5, 1, 2, 4, 8 hours). After the treatment, the sperm viability was calculated by hypo-osmotic swelling test. We selected 0, 50, 100 μM concentration during 0.5 hour as inhibitor treatment condition before in vitro fertilization. Next, we examined fertility and quantified aromatase protein in sperms with different density. In the first experiment, viability of sperm was decreased following the increasement of inhibitor concentration. The aromatase inhibited sperm showed lower penetration rate and cleavage rate than those of non-treated sperm. Concentration of 50 μM inhibitor had no significant effect on the sperm viability, but it significantly reduced sperm fertility. Second, sperms with low density showed higher penetration rate, but no significant difference between sperms with high density. In conclusion, aromatase is responsible for viability and fertility of porcine sperm similar to mouse and human, however, density of sperm has no correlation with quantity of aromatase protein.