Abstract: Calpastatin(CAST) has profound effects on the muscle growth and tenderness It was indicated that calpastatin could affect the protein metabolism of poultry In order to investigate the effect of calpastatin gene on muscle tenderness traits of chicken, the adequate quality broilers new strains bred by Sichuan Daheng pourty breed limited company were used．The single nucleotide polymorphisms (SNPs) were detected by PCR-SSCP and DNA sequencing．A SNP site（G→T） was found in coding region of CAST gene. The different genotypes detected by PCR-SSCP were defined as AA, BB and AB. Correlation between genetype and chicken muscle fiber traits was analyzed with SAS 8.01. The statistics analysis results showed that the CAST polymorphism was significant related to the muscle fiber density (MFN) and diameter (MFD)（P＜0.05）. And the chicken in identical day with the genotype of AA has a higher MFN and lower MFD than those with the genotype of AB（P＜0.05）, while there was no significant difference between the genetypes of BB and AA/AB（P＞0.05）. The chicken in identical body weight with the genotype of BB has a higher MFN and a lower MFD than those with the genotype of AB（P＜0.05）, while there was no significant difference between the genetypes of AA and AB/BB（P＞0.05） The results indicated that the CAST gene might play an important role in chicken muscle fiber formation. The significant correlation between CAST and development of muscle fiber suggested that this gene is a good marker in marker assisted selection program for muscle tenderness traits.