The increase of the bioterium’s production capacity and the quality of its products are a necessity due to the biological experimentation requirements. The identification of efficient selection criteria for the rodents could contribute to production optimization. An important trait for Wistar rats is litter size, over which there may be interference of sires’ scrotal measurements. Thus, the aim of this study was to evaluate the effect of scrotal length and width over litter size in Wistar rats. The measurements of the scrotal length and width of 27 sires at 60 days of age were made aiming at evaluating such effects over litter size at birth, by means of a nonparametric evaluation of the data. The correlations among these variables were also estimated. There was no significant effect of scrotal length and width, season at calving and dam age at calving over the variable litter size at birth (P > 0.05). The correlations obtained also did not indicate any association between litter size and the scrotal size of rats. We conclude that the selection of Wistar sires for scrotal size at 60 days of age is not an efficient strategy in order to improve litter size in the studied population. These results indicate that other factors may be involved in the variability in litter size at birth in this colony