In this paper, an additive manufacturing process, Magnetic Field-assisted Projection Stereolithography (M-PSL), is developed for 3D printing of three-dimensional (3D) smart polymer composites. The 3D printed magnetic field-responsive smart polymer composite creates a wide range of motions, opening up possibilities for various new applications, like sensing and actuation in soft robotics, biomedical devices, and autonomous systems. In the proposed M-PSL process, a certain amount of nano- or micro-sized ferromagnetic particles is deposited in liquid polymer by using a programmable micro-deposition nozzle. An external magnetic field is applied to direct the magnetic particles to the desired position, and to form the desired orientation and patterns. After that, a digital mask image is used to cure particles in photopolymer with desired distribution patterns. The magnetic-field-assisted projection stereolithography (M-PSL) manufacturing process planning, testbed and materials are discussed. Three test cases, an impeller, a two-wheel roller and a flexible film, were performed to verify and validate the feasibility and effectiveness of the proposed process. They were successfully fabricated and remote controls of the printed samples were demonstrated, showing the capability of printed smart polymer composites on performing desired functions.