Myostatin (MSTN), a member of the TGF-β superfamily, has been identified as a negative regulator of skeletal muscle mass. Inactivating mutations in the MSTN gene are responsible for the development of a hypermuscular phenotype. The aim of this study was to identify an effective small interfering RNA (siRNA) to knockdown the myostatin gene in sheep fibroblast cells. Four siRNAs targeting sheep myostatin were synthesized and tested. Quantitative RT-PCR showed that siRNA1, siRNA2, siRNA3, and siRNA5 significantly reduced myostatin transcript levels by 72, 68, 56, and 76 % (P < 0.05), respectively. Western blot analysis showed that myostatin protein expression was significantly reduced by 76 % using siRNA1 and by 65 % using siRNA5 (P < 0.05). Therefore, siRNA1 and siRNA5 may have the potential to knockdown myostatin gene expression and increase sheep meat production, which should be a focus of future studies.