The basal metabolic rate (BMR) was measured in the female KM mice(Mus musculus) prior to reproduction and at late lactation using a closed-circuit respirometer. Relationships between BMR,reproductive output and visceral organs were examined using Regression residuals and Pearson correlation analyses. It was showed that the BMR was 66% higher at late lactation than that prior to reproduction. There was no significant correlation between the BMR prior to reproduction and reproductive output. However,the BMR at late lactation was positively correlated with maternal body mass,food intake,litter size and mass,as well as the weight of visceral organs and gastrointestinal tract,within which the correlation between BMR and gastrointestinal tract was higher relative to the other visceral organs. Our data have provided support for the hypothesis that animals with high BMR during lactation might have a greater capacity for absorbing energy,and consequently have more energy export for reproductive output.