Calpastatin has been introduced as an effective candidate gene as regards growth efficiency and meat quality traits. Throughout the present study, blood sampling as well as carcass trait measurements were performed on 74 Lori-Bakhtiari sheep and on 40 Zel-Atabay cross-breds from industrial slaughterhouses of Shahrekord and Gorgan cities, respectively. Following DNA extaction, Polymerase Chain Reactions were performed for amplification of a 254 bp fragment containing the entire exon 6 of calpastatin gene. SSCP method along with silver staining were employed for genotyping of PCR products. Fourteen genotypic patterns namely: AA, BB, AB, AC, AD, BE, AF, AG, AH, AI, JJ, AJ, BK, and AL were observed with frequencies of 0.035, 0.123, 0.105, 0.114, 0.009, 0.053. 0.316, 0.027, 0.017, 0.017, 0.009, 0.105, 0.017, and 0.053, respectively for the two breeds. The calpastatin gene significantly affected live weight before slaughter, fat-tail weight(p<0.001), percentage of the fat-tail to carcass weights (p<0.01) as well as fat bearing carcass weight (p<0.05). Genotype AB was found as the superior genotype for all the traits. The favorable genotype for growth traits was AJ, whereas BE being the favorable one for weight and for percentage of fat-tail (animals with BE genotype bore a smaller fat-tail) but this genotype along with genotype BB were unfavorable as regards growth traits.