ObjectiveTo comparatively analyze the impact of intraperitoneal injection of acidic phosphate buffer solution at a late stage of gestation on the reproductive physiology in two inbred strains of C57BL/6J (B6) and BALB/c (B/c) mice. MethodsOne or two sisters were randomly mated with one brother in the same strain overnight, starting at the age of 10 weeks. The correlation of mating mode (1∶1 or 2∶1) and vaginal plug with pregnancy rate was observed. The pregnant dams were intraperitoneally injected with acidic phosphate buffer solution at 17.5^th day of their gestation (day 0=day post mating). The observation was carried out to detect the impact of the injection of acidic buffer on pregnant dams and their fetuses, and also the growth of the offspring from weaning to 8 weeks. ResultsThe pregnancy rate was higher in B6 than in B/c females regardless of mating mode (29.4% vs. 21.1% ［2∶1］, 33.2% vs. 29.7% ［1∶1］). The better way to accurately determine pregnancy was to examine the expanded belly combined with increased body weight from day 10 to 14 post-mating. Compared with the dams of B/c strain, the impact of the peritoneal injection on those of B6 strain was stronger. It manifested a reduction in number of weaned offspring (4.7±3.1 vs. 6.1±2.1), a significant decrease (P<0.05 in both genders) of the offspring''s body weight at the time of weaning in both genders (g,female:11.7±1.1 vs. 12.7±1.5; male:12.8±1.3 vs. 13.6±1.5), and a significantly different growth pattern of the offsprings (P=0.000). ConclusionsThere is a strain-dependent difference in some aspects of reproductive physiology in inbred mice. The tolerance to the intraperitoneal injection of acidic phosphate buffer solution at a late stage of gestation varied in the two strains. The procedure may produce some effect on dams'' breeding after baby-delivery, which may continue to influence the early developmental growth of the offspring.