The aim of this study was to evaluate the effect of supplementing a probiotic strain isolated from guinea pig intestinal microbiota on its performance during the growing and fattening period. A total of 80 male guinea pigs of one day old were distributed in 40 experimental units. Five treatments with eight replicates per treatment were used: T1, T2, and T3 received 100, 150 and 200 ml of probiotic respectively, and T4 y T5 were the positive and negative controls respectively. Dry matter intake (DMI), body weight gain, feed conversion ratio (FCR) and carcass yield were evaluated. T2 showed the lowest DMI (2564 g) and FCR (3.90) whereas T5 had the highest DMI (3293 g) and FCR (5.04). Body weight gain and weight and carcass yield were not affected by the probiotic. The dietary inclusion of probiotic strains from guinea pig intestinal microbiota significantly affect (p<0.05) feed conversion ratio in growing and fattening guinea pigs.