Animals may use different reproductive strategies depending on environmental conditions. This study investigated the effects of maternal stress induced by exposure to predator odors on reproductive output and adult offspring quality in pregnant Brandt’s voles (Lasiopodomys brandtii). We exposed pregnant Brandt’s voles to cat urine, rabbit urine, or distilled water for 18 days (1 h/day). Our results indicated that pregnant voles in the cat odor-exposed group tended to produce more offspring and the number of viable female offspring was larger. However, we did not observe any differences in the sex ratios of vole offspring among the three treatment groups. Compared with the control (distilled water) group, female offspring of voles in the cat odor-exposed group had lower body weights, lengths, and smaller body weights in relation to body length, whereas they had larger ovaries in relation to body weight. Furthermore, the female offspring of the voles exposed to the cat odor had higher concentrations of serum estradiol and higher levels of gonadotropin-releasing hormone mRNA in the hypothalamus compared with the female offspring of the voles in the control group. However, we observed no differences among the male offspring in the three treatment groups. Our findings suggest that pregnant Brandt’s voles suffering from chronic exposure to predator odors will produce greater numbers of low-weight female offspring that probably possess higher breeding potential to improve the fitness via regulation of the hypothalamic-pituitary-gonadal axis.