More substances leaked from a higher-vigor seed sample than from a lower-vigor sample. This indicates that, in some cases, electric conductivity does not represent seed vigor level very well, especially for high-vigor seeds. Results from germination, germination index, leachate conductivity, and the ratio of K+/Na+ from three-seed lots of Chinese cabbage (Brassica pekinensis (Louv.) Rupr) showed that K+/Na+correlated well with germination and germination index. The ability of K+/Na+ to indicate well changes in vigor was further supported by investigation in soybean (Glycine max (L.) Merr.) seeds and another cultivar of Chinese cabbage seeds. Thus, seed leakage of K+/Na+ can accurately indicate seed vigor, whereas the conductivity test failed to do so. Furthermore, K+/Na+ showed up bigger quantitative differences in vigor level than did the conductivity test. This findings provide a more sensitive and accurate index for the assessment of seed vigor. The mechanisms of Na+ and K+ ion transport are also discussed.