Abstract： The goal of the present study was to investigate the effects of quercetin-filled phosphatidylcholine fiposomes (PCL-Q) on the currents carried by large conductance CaCa-dependent K+ channels (BKCa) in rat thoracic aorta following non-fatal whole-body ionizing irradiation. Using patch-clamp technique, it is found that the outward K+ currents of isolated smooth muscle cells (SMCs)stimulated by depolarizing voltage steps were sensitive to BKCa inhibitor, paxilline, and this kind of outward K+ currents in SMCs from irradiated animals demonstrated a significant decrease in amplitude. Radiation-induced BKCa suppression was evident 9 days post-irradiation and progressively increased over 30 days of experimental period. Thus, the vasorelaxing force of these SMCs may be diminished following irradiation. PCL-Q effectively restored BKCa function in post-irradiated SMCs. It is noteworthy that the constituents of PCL-Q, i.e., free quercetin (Q) and "empty" liposomes (PCL), being taken separately, showed a decreased ability to recover BKCa function as compared with combined composition. These results suggest that PCL-Q is able to regain normal function of BKCa following irradiation. The protective effects of PCL-Q can be explained by its antioxidant and membrane repairing properties as well as its ability to inhibit protein kinase C activity. Thus, the lipid encapsulation of flavonoid, PCL-Q, appears to be a potential medication in the case of ionizing irradiation accident, and for the patients with neoplasm who have to receive external radiotherapy as well.