Myostatin (MSTN), a protein encoded by growth differentiation factor 8 (GDF8), is primarily expressed in skeletal muscle and negatively regulates the development and regeneration of muscle. Accordingly, myostatin-deficient animals exhibit a double-muscling phenotype. The CRISPR/Cas9 system has proven to be an efficient genome-editing tool and has been applied to gene modification in cells from many model organisms such as Drosophila melanogaster, zebrafish, mouse, rat, sheep, and human. Here, we edited the GDF8 gene in fibroblasts and embryos of Debao pig and swamp buffalo using the CRISPR/Cas9 system. The CRISPR/Cas9-mediated mutation efficiency in fibroblasts was as high as 87.5% in pig and 78.9% in buffalo. We then obtained single-cell clones with mutations at the specific sites of the GDF8 gene by screening with G418 in fibroblasts of pig and buffalo. In addition, the frequencies of Cas9/gRNA-mediated mutations were at 36 and 25% in the intracytoplasmic sperm injection embryos of pig and in vitro fertilization embryos of buffalo, respectively. Our work demonstrates that the Cas9/gRNA system is a highly efficient and fast tool for genome editing in cultured cells and embryos of Debao pig and swamp buffalo. These results can be helpful for the establishment of a new animal strain that can generate more meat.