Microbial induction of rusty-root was proved in this study. The enzymes hydrolyzing plant structural materials, including pectinase, pectolyase, ligninase, and cellulase, caused the rusty-root in ginseng. Pectinase and pectolyase produced the highest rusty-color formation. Ferrous ion ($Fe^{+++}$) caused the synergistic effect on rusty-root formation in ginseng when it was used with pectinase. The effect of ferric ion ($Fe^{++}$) on rusty-root formation was slow, compared with $Fe^{+++}$, probably due to gradual oxidation to $Fe^{+++}$. Other metal ions including the ferric ion ($Fe^{++}$) did not affect rusty-root formation. The endophytic bacteria Agrobacterium tumefaciens, Lysobacter gummosus, Pseudomonas veronii, Pseudomonas marginalis, Rhodococcus erythropolis, and Rhodococcus globerulus, and the rotten-root forming phytophathogenic fungus Cylindrocarpon destructans, caused rusty-root. The polyphenol formation (rusty color) was not significantly different between microorganisms. The rotten-root-forming C. destructans produced large quantities of external cellulase activity (${approx}2.3$ U[${mu}m$/min/mg protein]), which indicated the pathogenecity of the fungus, whereas the bacteria produced 0.1-0.7 U. The fungal external pectinase activities (0.05 U) and rusty-root formation activity were similar to those of the bacteria. In this report, we proved that microbial hydrolyzing enzymes caused rusty-root (Hue value $15^{circ}$) of ginseng, and ferrous ion worsened the symptom.