This article discusses the struggle of Nias people (Ono Niha), who are one of the oldest tribes inhabiting Nias Island, about the world of the dead. On the one hand, Ono Niha has a high culture and a belief system that has been lived thousands of years from generation to generation. But on the other hand, since 1865, through the Gospel Message by RMG and NLG, Ono Niha gradually became a follower of Christ. However, despite more than 150 years of Christianity in Nias, Ono Niha struggles with the Christian faith. One of the struggles of the faith of the church's people is related to the world of the dead. What is death? Right, do spirits enter the world community of the dead? In reality, Ono Niha, who is still faithful in carrying out his customs, still believes that the spirits of ancestors are blessings or can be angry and bring curses if his descendants do not meet the demands of the ancestors when they live. Another problem is the occurrence of possession or possessiveness experienced by the citizens of the congregation, both adults and teenagers. Here there is a conflict in Ono Niha because the church understands that all elements of the old belief are elements of disbelief and classified as occult. But on the other hand, Ono Niha still believes and lives it. To know Ono Niha's belief system about the world of the dead, this article will be presented an understanding of the human self according to Ono Niha and Ono Niha's belief in death and the world of the dead. At the end of the paper, we explain the interaction and impact of Ono Niha’s old cultural and religious encounters with Christianity.