For spherical mechanisms, instantaneous poles are as the counterparts of instant centers in planar mechanisms. However, they are not fully exploited to study the kinematic behavior of spherical mechanisms as the instant centers are for planar ones. The main purpose of this paper is the singularity analysis of multi-degree-of-freedom (DOF) spherical mechanisms. After reviewing the concepts of spherical motion and instantaneous poles, a geometrical technique is presented to identify the singularities of the mechanisms using the properties of instantaneous poles. The method is fast and comprehensive that can be easily employed for all types of multi-DOF spherical mechanisms. Two illustrative examples are included to show the effectiveness of the presented method and the obtained singularities are verified analytically.