Abstract: After being treated by electrical stimulation in yak meat,changes in microstructure and myofibrillar proteolysis were studied.The raw materials were yaks slaughtered with electrical stimulation within 5min( 21 V,50Hz,90s),and then chilled( 0~4℃,wind speed 0.5m / s).Taking front triceps( TB),central longissimus muscle( ML) and posterior semimembranosus( SM) as material,respectively,then determined sarcomere length,muscle fiber diameter,MFI value,muscle fiber microstructures and SDS- PAGE electrophoresis after postmortem 0,1,3 and 5d.The results indicated that after electrical stimulation,sarcomere length of different parts of yak meat changed significantly( p < 0.05); the average diameter of the muscle fibers shortened 6%,5% and 9% repectively,MFI values increased by 54%,55% and 92% significantly,tenderness of SM increased significantly( p < 0.05).Share of different parts of yak meat myofibrillar ultrastructure contracture were 23.9%,26.3% and 31.2%. Myofibrillar ultrastructural changed significantly. The view of the SDS- PAGEphotograph,TB,ML and SM Myofibrillar protein degradated completely between 48~75ku. In a conclusion,electrical stimulation could shorten the aging time,and improve tenderness of yak meat,especially,make a significant difference to poorer SM part( p < 0.05).