Abstract: Using the common antioxidant Vc as control group, main ingredients and the antioxidant activity in vivo and in vitro of acorn shell pigment were researched in order to provide a theoretical basis for the development and utilization on antioxidant function of acorn shells. The results showed that the acorn shell pigment contained an abundance of polyphenols and flavones, the total content of polyphenols was 27.8%, and he total content of flavones was 8.6%. The antioxidant experiment in vitro showed that the DPPH free radical scavenging ability and the Fe³⁺ reduction ability of acorn shell pigment performed a positive correlation with the increase of its concentration, in which, the half effective dose (IC₅₀=10 μg/mL) was higher than Vc group (IC₅₀=5 μg/mL), and it could reach the scavenging ability of Vc once the concentration of acorn shell pigment was around 40 μg/mL; when the concentration of acorn shell pigment was 1 mg/mL, the reduction ability of it (A_{710 nm} was 0.98) was nearly to Vc(A_{710 nm} was 1.17). In vivo antioxidant experiment, it used ⁶⁰Coγ irradiating the mice to establish an oxidative stress mice model except the blank group to analyze the antioxidant capacity of each group. The results showed that, to compare with the blank group, the body weight and the quality of organs of mice of model group had significantly decreased (P < 0.05), and it showed a bad phenomenon as loss of appetite, listlessness and so on, which indicated the oxidative stress model was succeed. The organ quality of acorn shell pigment group was significantly higher than the group of mice model (P < 0.05), but had no significantly different with the below blank group (P>0.05). It indicated that the acorn shell pigment had certain repair function to the mice organs irradiated by⁶⁰COγ. The results of the determination of the antioxidant enzymes and the oxidation products in the serum of the test mice further showed that, the low, medium and high dose groups of acorn shell pigment could all improve the activity of SOD and CAT in mice serum and reduce the content of MAD significantly (P < 0.05). Meanwhile, the 100 mg/(kg·day) dosage acorn shell pigment had the best effect on antioxidant activity in vitro which was similar to the group of Vc. In summary, the acorn shell pigment had antioxidant activity in vitro and in vivo, the 100 mg/(kg·day) group of acorn shell pigment could be equaled with the same dose of Vc on antioxidant effect, which had a good application prospect as an natural antioxidant.