If a part of a mechanism is restrained to rotate about a point not physically belonging to it, the mechanism is called a remote center-of-motion (RCM) mechanism. The RCM mechanisms are generally designed especially for robot-assisted minimally invasive surgery (MIS) systems, for which great progress has been made in recent years. An RCM mechanism type synthesis method is proposed in this paper by generalizing the intersection of motion planes. The existence of such motion planes is the fundamental feature of the classic Sarrus mechanism, for instance. The basic principle of the type synthesis method is to combine some typical planar mechanisms where their respective motion planes are free to tilt. Hence, the intersection line varies as the planes tilt. There is one invariant point on this intersection line, however, and this is the RCM point. The proposed method is used to design a class of spatial RCM mechanisms. And the kinematic characteristics of them are presented in this paper. In particular, several fully parallel two degree-of-freedom (DOF) RCM mechanisms and a 1-DOF RCM mechanism are considered in detail. Two spatial 3-DOF overconstrained RCM mechanisms are also obtained by the proposed method.