The influence of Capillaria hepatica on the breeding parameters of female Brandt′s Vole (Lasiopodomys brandtii) was investigated in typical steppe in Abagaqi, Inner Mongolia in May 2005. Standard killing trap method was used to capture rodents, then dissected to determine the infection of C. hepatica. We recorded the rodents′ species, body length, body mass, carcass mass, reproductive characteristics and the infection of C. hepatica. As body mass of rodents is one indicator of age, we chose those females with body mass between 25.1﹣55.0 g as the analysis sample, based on the previous research data of this rodent species about its reproductive characteristics. We compared and analyzed the relationship between the infection situation of C. hepatica and the pregnancy rate by Chi-square test and the relationship between the infection situation and the number of fetuses by T test for the females in the same and different mass (age) group (Table 1 & 2). The pregnancy rate of the infected group was slightly lower than those uninfected group. The pregnancy rate was 59.1% and 64.5% for those weighed 25.1﹣35.0 g mass (age) group, 57.7% and 67.6% for 35.1﹣45.0 g mass (age) group, 65.2% and 67.8% for 45.1﹣55.0 g body mass (age) group. No significant correlation (P > 0.05) was detected between the infection situation and the pregnancy rate, however the number of fetuses for the infected group was less than the uninfected group, and the infection situation was significantly correlated with the number of fetuses (P < 0.05). The results indicated that the infection situation of C. hepatica had no significant effect on the pregnancy rate of Brandt′s Voles, but produced a negative effect on the number of fetuses on Brandt′s Voles.