The use of autochthonous breeds as a base for alternative animal production supposes a real possibility for their recovery and conservation. Therefore, the present study analyses the growth and carcass characteristics of improved chickens of the Castellana Negra breed slaughtered at 18 weeks and for F1 crossbred chickens of improved hens of the Castellana Negra breed, and improved cocks of the Penedesenca Negra breed slaughtered at 12 weeks (young crossbred) and 18 weeks of age (adult crossbred), in order to compare to purebred and crossbred specimens at the similar weight (Castellana Negra and young crossbred), so as to compare purebred and crossbred animals at the same age (Castellana Negra and adult crossbred). The crossbred type presented a greater speed of growth rate and a weight which was significantly heavier than the Castellana Negra at 18 weeks. Too they presented faster average daily weight gain between 8-10 weeks (36.11 g/day), as well as the Castellana Negra (24.32 g/day), not having differences at feed conversion rates from different ages. The adult crossbred was the one which showed greater yield and carcass weight, as in drumsticks and thighs, but with no differences were detected in the breast or abdominal fat with the young crossbred type, although there were differences with the Castellana Negra. The young crossbred also presented further wings yield, as well as greater angle of breast and length of the carcass, but the viscera and abdominal fat content was also higher, although in the latter case was not different from that found in the adult crossbred content. Measures undertaken in noble parts (drumsticks, thighs and breast), in all cases values were higher in the adult crossbred.