Volatile oil from Lycium ruthenicum was extracted by steam distillation and its antioxidant activities in vitro were evaluated by scavenging capacity against DPPH free radical, hydroxyl free radical and ABTS free radical, with ascorbic acid (V–C) as the positive control. Then the chemical constituent of the volatile oil were analyzed by gas chromatography-mass spectrometry (GC–MS). The results showed that: 38 components were isolated and identified from the volatile oil. The main compounds in the volatile oils were linolic acid, Palmitic acid, elaidic acid, 2,3-dihydrobenzofuran, methyl linoleate, 2-methoxy-4-vinyphonol. The acids and esters were the dominant components in the essential oils(which occupied 85.696% of total constituents); the IC50 value of scavenging against DPPH free radical, hydroxyl free radical and ABTS free radical were 0.002 21, 0.007 68, 0.000 09 μg/μL, respectively. The antioxidation of volatile oils in vitro had a relation of concentration-dependent.