This study was to investigate effect of tunicamycin (TM) on sperm viability, mitochondrial activity and motility in boar semen. Collected sperm were incubated with semen extender containing 0, 1, 2, and 5 μM TM for 3, 6 and 9 h. Sperm viability was analyzed using SYBR14/PI doubling staining, and mitochondrial activity was detected using Rhodamine123/PI staining methods. Sperm viability, mitochondrial activity and motility were measured every 3 h during incubation. In results, boar sperm viability, mitochondrial activity and motility were significantly decreased in 2 and 5 μM TM groups compare to control group at all incubation time (p<0.05). In addition, mitochondrial activity and motility were significantly decreased in 1, 2, and 5 μM TM groups compare to control group at 9 h after incubation (p<0.05). These results suggest that TM can inhibit sperm viability, mitochondrial activity and motility in boar semen, and it may influence on the fertility of sperm.