Abstract: To investigate the molecular mechanism for yak to adapt the hypoxia environment of plateau, experiments were carried out to measure myoglobin concentration, activities of lactate dehydrogenase(LDH) and malate dehydrogenase(MDH) in heart and skeletal muscles of yak. Also, yak myoglobin was purified and its gene was cloned and sequenced. Yak heart muscle and skeletal muscle contained significantly higher concentration of myoglobin than buffalo and yellow cattles. Heart tissues had significantly higher content of myoglobin and MDH/LDH ratio than skeletal muscles (P<0.01) in yak, yellow cattle and buffalo. Heart MDH/LDH ratio in yak was significantly higher than those of buffalo and yellow cattle, however, skeletal muscle MDH/LDH ratio showed no difference among the species tested. Significant positive relationship between myoglobin content and MDH/LDH ratio was observed in heart and skeletal muscles. The full-length coding sequence of yak myoglobin was cloned by RT-PCR using total RNA extracted from heart muscle of Maiwa yak.The amplified yak myoglobin gene shares 995% homology with that of bovine and the same amino acid sequence. Myoglobin was purified from yak heart muscle by salting-out, CM-Sephadex cation exchange chromatography, and Sephadex G-50 gel chromatography.The molecular weight of purified yak myoglobin was approximately 17 ku as shown on SDS-gel.