The development of tissue composition during growth may be reflected in the carcass tissue composition due to age at slaughter and sex. For this reason, the aim of this work is to analyze the carcass composition in 6 different carcass cuts, in males and females fattening or discarded guinea pigs. Forty guinea pig carcasses were selected: 20 from 3-mo-age fattening animals (10 males and 10 females) and 20 from 12-mo-age breeding discarded animals (10 males and 10 females). Each carcass was divided into 2 half carcasses; the right half carcass was jointed in 2 cuts following a technical standard commercial regulation from Peru (forequarter and hindquarter), and the left half carcass was jointed in 4 cuts following anatomical points (neck, shoulder, hind leg and ribs). Each cut was dissected in skin, muscle, sub-cutaneous fat, inter-muscular fat, waste and bone. Total fat was calculated as the sum of sub-cutaneous and inter-muscular fat, inedible section as the sum of bones and remainder, and muscle + freeze-thawing loss. All results are presented in tissue weights of the cut or whole carcass. A factorial ANOVA procedure was used with the statistical program SAS (v. 11), comparing among the different cuts, and analyzing the effect of age and sex. For the whole carcass composition, 3 mo-age guinea pigs showed the lowest fat content and female 12 mo-age animals the highest value. For muscle, bones, skin and waste, 12 mo-age guinea pigs had higher values in carcass than the younger animals, and no differences were found due to the sex. Into the 4 cuts jointing method, long leg and ribs cuts had the higher values of fat, muscle, bones and skin, while ribs presented the highest waste content. And into the commercial jointing method, the forequarter showed the highest contents of all the analyzed tissues. We conclude that tissue composition in the whole carcass is different in fattening or discarded guinea pigs, except for the fat content, in this case, 3 mo-age females have similar values than discarded guinea pigs.