The aim of this study was to investigate relationship among seed viability and enzymes activities involved in scavenging reactive oxygen species (ROS), especially, superoxide dismutase (SOD), glutathione reductase (GR), and catalase (CAT). In other respects, osmopriming has been demonstrated to reinvigorate aged seeds. Various viabilities of seeds that were ranged from 80 to 100% of germination rate could be produced using osmopriming and accelerated aging treatments. Priming treatment of Pinus thunbergii seeds for 3 days at $15^{circ}C$ with a polyethylene glycol solution at -1.2 MPa improved their subsequent germination at $25^{circ}C$. Accelerated aging (3, 6, 9, and 12 days at $41^{circ}C$ and 100% relative humidity) decreased seed germination percentage depending on aging treatment duration. Electrolyte conductivities of seeds were measured as assay of membrane integrity. The conductivity from electrolyte leakage of P. thunbergii seed was also correlated with seed germinability. Conductivity for control seeds that had 95% of germination percentage was 3.48 ${mu}S;g^{-1}$, but jumped as doubled (7.98 ${mu}S;g^{-1}$) in 12-day-aged seed that had 80% of germination percentage. Our results demonstrate that aging of P. thunbergii seeds is associated with changes in the electrolyte leakage, lipid peroxidation, and antioxidant defense system. Priming of aged seeds progressively restored the initial germinative ability and resulted in a marked decrease in the levels of MDA and conductivity of seed leachate. These effects of priming were also well recovered of GR and CAT activities in aged seed. The improved seed quality by priming treatment appears at least partly attributable to reduced lipid peroxidation, resulting from enhanced antioxidative enzyme activities that are suggesting the antioxidant defense systems play a key role in seed vigor.