幻影说（英语：Docetism），又称看似人主义，或称唯神主义，是早期基督教对基督的表述之一。此派认为，耶稣是个完全的神，不可能成为肉身。耶稣的本体就是上帝，耶稣在人间的一切活动，包括十字架上受苦，以及而后的复活、升天，都只是化身及假象，只是上帝投射在人间的一个影子、幻象或幻影形体。因此他们反对道成肉身理论。

传统上认为，此派与诺斯底主义及希腊哲学关系密切，在基督教会中，马吉安是第一个提出这个学说的人。325年尼西亚会议宣布幻影说为异端，此派因而衰微。

In Christian terminology, docetism (from the Greek δοκεῖν/δόκησις dokeĩn (to seem) /dókēsis (apparition, phantom), according to Norbert Brox, is defined narrowly as "the doctrine according to which the phenomenon of Christ, his historical and bodily existence, and thus above all the human form of Jesus, was altogether mere semblance without any true reality." Broadly it is taken as the belief that Jesus only seemed to be human, and that his human form was an illusion. The word Δοκηταί Dokētaí (illusionists) referring to early groups who denied Jesus' humanity, first occurred in a letter by Bishop Serapion of Antioch (197–203), who discovered the doctrine in the Gospel of Peter, during a pastoral visit to a Christian community using it in Rhosus, and later condemned it as a forgery. It appears to have arisen over theological contentions concerning the meaning, figurative or literal, of a sentence from the Gospel of John: "the Word was made Flesh".