Abstract: White root rot in Delonix regia was a disease found in recent years in Panzhihua City. There was no formal report on the disease so far. The disease was found usually in lateral and fine roots of Delonix regia. The infection of the disease could cause big trees of 10 years or more to fall down when storm passed by, resulting in much trouble to urban traffic. The pathogen of this disease was Rosalinia necatrix. The corridium and ascospore were invisible while hypha and rhizomorph could be seen in natural condition. The rhizomorph was white and feathery and appeared in root surface. The sclerotium was rarely seen. The suggested methods for controlling this disease included spraying bactericide and germicide to rhizosphear and branches, and strengthening tending and management.