As is often mentioned in his biographical studies, William James was greatly attracted to spiritual phenomena and continued psychical research to his last days. He conducted experiments with a trance medium, Mrs. Piper, whose mediumship was so strong that he was convinced of the genuineness of the phenomena. Although he arrived at no conclusive view on the spiritual matter, his thinking was greatly affected by psychical research. In this paper its effects are discussed in some respects. <br>First James saw in psychical research a solution to the contemporary problem of how to settle the struggle between science and religion. He criticized mechanical rationalism and contrived a framework of the new science which would defend the value of personal experience. Secondly, influenced by his fellow psychical researcher F. W. H. Myers, James employed the subliminal-self theory, which says that everyone has a wider self under the realm of consciousness. This theory assured him of the possibility of telepathy, but at the same time it brought some contradiction to his own "stream of thought" theory that denies substantial beings in the mind, such as the soul. Moreover, as a result of his last experiments, James came near to believing in the existence of the soul. But unlike Myers he remained doubtful to the last because of his thirst for truth.