The author presents forms of diagnoses and the healing of illnesses according to the belief and faith in supernatural powers, ancestors’ spirits and ghosts of the Lisu. These supernatural beings can bring benefit or harm to human beings if humans are sacrilegious to or violate traditional norms and practices relating to daily life. The author uses case studies of sicknesses with unknown causes, showing diagnoses according to the Lisu’s beliefs and wisdom and the logic of the social relationship to those beliefs as well as explaining the concepts of mind, spirits or animistic beliefs, bilateral logic and polarities of sicknesses. Initially, sicknesses were believed to be caused by spirits, be it ancestors’ spirits regulating the morality, traditions and customs of their children, spirits dwelling in nature which were looked down upon, black magic from enemies, or other bad spirits or witches. Ancestors’ spirits were asked to possess mediums in order to identify causes or symptoms, so that healing could be conducted correctly. Sometimes the ritual was repeated because the sick had not recovered, indicating wrong diagnosis. If the sickness persisted, modern medical treatments were sought after, which was due to the influence in Christianity of some villages.