Abstract: Meat from yak (Bos grunniens) is a primary staple in diets of people in western China. Yak meat has low-fat content, high protein and good amino acid and fatty acid profiles. However, meat from yak may be less tender than meat from Bos taurus cattle. Gannan Black yaks (n = 181) were used to investigate the effects of age at harvest and aging days on meat quality characteristics of M. longissimus dorsi. Yaks were harvested at 2, 3 and 4 year of age and muscles of each yak carcass were aged for 0, 1, 3, 7, 14 or 21 days at 4°C and frozen at -20°C until analyzed. Age at harvest affected shear force and percentage fat, protein and moisture (p<0.05). Aging days affected shear force, retort cooking loss, pressing loss, moist cooking loss, pH, percentage fat, moisture (p<0.01) and protein (p<0.10). There were interactions between aging days and age at harvest for shear force, moisture and protein (p<0.01). Aging days appeared to have a greater effect on shear force than age at harvest and tended to moderate the age at harvest effect on shear force. When cooked in retortable bags, cooking loss decreased until 3 days postmortem after which it remained relatively constant. When steam cooked, meat aged 7 days had the lowest cooking loss (p<0.05). Pressing loss decreased until 3 days postmortem then remained relatively constant. After thawing, pH decreased during the 21 days period of postmortem aging with the greatest decline in the first 24 h (6.68-5.73 from 2-24 h postmortem). Results suggest that aging yak meat 7 days is sufficient for acceptable tenderness and meat quality.