Abstract: To investigate the relationship between the polymorphisms of the microsatellites and the Longissimus dorsi (L. dorsi) traits, ten highly polymorphic microsatellite loci which probably be linked with the Carwell gene were selected from the genetic linkage map of chromosome 18 in sheep. The polymorphisms of these microsatellites were detected, and the genetic character was analysed in two grading crossing sheep group(F2 from Dorset♂and Suffolk♂×Xinjiang fine wool sheep♀,respectively ) with nondenaturing polyacrylamide gel electrophoresis by multiplex silver staining. Results showed that there were differences for genetic parameters between the two meat sheep groups among these loci . The effect of these loci on L. dorsi traits were analyzed in a generalized linear model(GLM). Results indicated that : (1) The effect of BM3413 on thickness of L. dorsi reached a significant level at P<0.05 , and TGLA122 had a significant effect on width of L. dorsi (P<0.05) , respectively; The locus MCMA26 had a significant impact on thickness, width and area of L dorsi traits (P<0.05) in the Dorset group, respectively. While the other loci(ILSTS54, TGLA337, HH47, TGLA122, BP33, MCM38 and CSSM18 ) had no impact on the L dorsi traits (P>0.05) in the same group; (2) In the Suffolk population, the loci of MCM38, CSSM18, ILSTS54 and BM3413 each had a significant impact on all the three L. dorsi traits simultaneously (P<0.05 or P<0.01 ); And the other 6 loci( TGLA337, HH47, TGLA122, BP33, OB2 and MCMA26 ) had no effect (P>0.05) in the same group. We also found that, 196 bp/222 bp and 192 bp/220 bp at MCMA26 were the most favourable genotypes for area of L. dorsi in the Dorset group; 124 bp/134 bp at CSSM18, 130 bp/148 bp and 134 bp/148 bp at ILSTS54 , 190 bp/232 bp at BM3413 were the most favourable genotypes for area of L. dorsi in the Suffolk group. Two conclusions were drew : (1) The Carwell gene probably located in the region of MCMA26- CSSM18, and there may be a new gene or QTLs (quantitative trait loci) flanking the locus BM3413; (2) The most favourable genotypes we found may be regarded as the candidateloci for the marker -assisted selection or markerassisted breeding in the merit meat sheep on early period.