Objective To study the life span of Trichinella spiralis male adult and its effect on female fertility. Methods 22 Kunming mice were divided into three groups. Group A was orally inoculated by encysted larvae， dissected at day 5， 10， 20， and 30 post infection， adult worms were then collected and counted. Group B was fed with 5-day adults （70 females + 30 males/mouse）. Group C was fed with 5-day females （70/mouse） only. Groups B and C were sacrificed 30 days post inoculation， larvae were collected to calculate reproductive capacity index （RCI）. Male worms of day 5， 10， 20 and 30 were fixed in glutaraldehyde for scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Results 20 days after infection， there were more males than females in the intestines of group A mice （female ∶ male =1 ∶ 1.3）， but much more males than females on the 30th day after infection （female ∶ male =1 ∶ 8.5）. Mice of groups B and C were infected by 5-day adults successfully with a RCI of 154.90±2.62 and 13.77±1.67 respectively（t=111.26， P＜0.01）. SEM revealed the copulatory bell of 5-day male adult， alae erected， and genital pore uncovered； while alae of 20-day male collapsed， genital pore was covered. Under TEM， there were large number of mature sperms within spermaductus of 5-day and 10-day males， but only a few immature sperms in the testis of 20-day and 30-day males. Conclusion Male adults can survive longer than one month in host. 5-day female and male adults and 5-day females can infect mice orally， with a significantly higher fertility in the former.