The aim of this study was to estimate genetic parameters for birth and weaning weight in guinea pigs (Cavia porcellus) reared in a farm in Cieneguilla, Lima, Peru. Univariate animal model that included sex of calf, parity, season of birth, animal and litter effect was used in the genetic analyses. In addition, the effect of number of newborns was included in the model for birth weight, and the number of born alive and age at weaning were included in the model for weaning weight. Variance components were estimated by Bayesian Gibbs sampling with a chain of 100 000 rounds with the first 10 000 rounds discarded for burnin by using MCMCglmm library of R software. Heritability estimates for birth weight was 0.155 ± 0.036 and for weaning weight was 0.246 ± 0.046. These values were similar to those estimated by using REML.