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Biological joints have advantages such as compact structure and multi degree-of-freedom (DOF) rotation. To emulate a biological joint, a 2-DOF rotary joint actuated by dielectric elastomer (DE) is designed, in which DE acts as muscles. Based on the analysis of the working principle of the joint, a mechanism is presented to increase its angular displacement. The moment produced by the mechanism increases with increasing rotary angle, and is favorable to the increase in angular displacement. Experiments show that the joint can rotate back and forth with 2 DOFs, and the deflection angles around two axes can be heightened to more than 18°, which evaluates the feasibility of the proposed mechanism, while the blocking moment is not influenced. After further improvement, the 2-DOF rotary joint can be used in some bionic robots, such as robot fishes and robot snakes.