This study was aimed to develop a new formula for herbal medicine-safety classification in terms of evidence-based medicine. Recently, human equivalent dose(HED)-based therapeutic index was developed for herbal medicine-safety classification by transforming $LD_{50}$ to HED. However, the use of the $ED_{50}$ and $LD_{50}$ to derive the therapeutic index may be misleading as to safety, depending on the slope of the dose-response curves for therapeutic and lethal effects. To overcome this deficiency, HED-based MOS(Margin of Safety)was developed and suggested in this study. The HED-based MOS developed by using $LD_1$, changing to ALD(approximate lethal dose), and $ED_{99}$. The HED-based MOS seems to be more useful and safer than HED-based therapeutic index since its values for several herbal medicines are basically two times less than the values from HED-based therapeutic index. Thus, HED-based MOS can be a good example of Evidence-based approach for herbal medicine-safety classification.