To investigate the protective effect of Bulbus Allii Macrostemi (BAM) on the damage by pulmonary vascular endothelial cells by xanthine oxidase (XO)/hypoxanthine (HX)-induced oxygen free radical, Neutral Red (NR) and protein kinase c (PKC) activity assay were used. The results were obtained as follows ; The viability of vascular endothelial cells treated with XO/HX was decreased. And activation of PKC represented a maximal increase in group treated with XO/HX for 15 mins in vasvular pulmonary endothelial cells. But pretreated groups with BAM extracts were not inhibited the increase of PKC activation by XO/HX in a dose-dependent fashion. These results show that XO/HX elicits toxic effects in cultured pulmonary vascular endothelial cells, and suggest that BAM extract is very effective in the prevention of XO/HX-induced PKC activation.