Abstract: In order to study the basic blood indexes of artificially bred yellowfin tuna (Thunnus albacares), we determined the concentrations or activities of albumin, triglyceride, total cholesterol, transaminase, lysozyme and phosphatase in its serum (W1: 400−900 g; W2: 900−1 400 g; W3: 1 400−1 900 g) with different body mass. The results show that there were significant differences among the albumin, triglyceride and aspertate aminotransferase groups (P<0.05). The glutamic pyruvic transaminase activity and total cholesterol concentration in W2 group were significantly lower than those in the other two groups (P<0.05). The decending order of the concentrations of albumin, triglyceride and total cholesterol was W3>W1>W2. There was no significant difference in the alkaline phosphatase activity among the groups (P>0.05). The acid phosphatase activity in W1 group was significantly higher than that in the other two groups (P<0.05), and the lysozyme concentration in W1 group was not significantly different from that in the other two groups (P>0.05). The results reveal that there were differences in the blood indexes among the three groups of different mass; the difference between W2 group and the other two groups was greater, and the difference between W1 group and W3 group was smaller.