Mature body size and weight of sheep are important traits that significantly influence mutton yield and economic benefits of sheep farming. The exploration for key genes underlying these traits will facilitate the advancement of molecular breeding in meat sheep. In this study, key candidate genes for five body size traits and the body weight were identified in mature Huameng meat sheep through GWAS and ROH analysis. After quality control, 451 individuals and 16 751 761 variants were analyzed using EMMAX software in a linear mixed model (LMM). A total of 3 genome-wide and 35 chromosome-wide significant SNPs were identified, respectively. Several key candidate genes have been uncovered, including ZFAT, ACSL3, and GRID2 for cannon bone circumference; UNC5C and BMPR1B for body weight and chest girth; PCDH15 and NUP93 for hip width; and PTPRD for body height. ROH analysis revealed a high-frequency ROH hotspot region on chrX. In addition, ROH analysis suggested that inbreeding may lead to a significant depression in body height of sheep. This study provides important clues for revealing the molecular mechanisms underlying sheep body morphological traits and identifies key candidate genes for molecular breeding in meat sheep.