The soils of mulberry fields infected with and without root-rot, were examined to identify pedological causes, if any, in the incidences of root-rot in Nakhon Ratchasima of Northeast Thailand. The results obtained showed that the causes of mulberry root-rot were associated with topographical factors and physical and chemical properties of soils. Among them, the following factors were of particular significance: one was the location near the foot of a gentle concave slope, where water tends to stagnate; and the other was the existence of an impermeable layer in the subsoil, which interfered percolation of water to a lower part of the profile. These factors caused a serious air-deficiency under the extremely wet condition after heavy rainfalls. In addition, a large amount of exchangeable Al appeared to adversely affect the root growth. It is therefore concluded that the root-rot incidences in Northeast Thailand are closely related to pedological status.