This paper proposes a haptic interface for simulation of endoscopic endonasal skull base surgery. Requirements of the haptic interface are derived by analyzing six surgical procedures selected by a surgeon. The haptic interface consists of two symmetrical haptic units which have 7 DOF input and 3 DOF output individually. The spherical mechanism is applied to render high force and high stiffness. The required torque of motors is 2427.8 N⋅mm, 1358.9 N⋅mm, 3829.0 N⋅mm to provide maximum 24 N. The stiffness of the haptic interface is analyzed to be 9.96 N/mm. The safety of the haptic interface is analyzed to be higher than 2. A force sensor is used to compensate the friction and inertia of the haptic interface. The force felt by the user in the free motion decreased by maximum 89.9 %. It is confirmed through experiments that the stiffness of 8.9 N/mm and the force of 24 N can be rendered. The haptic interface has at least 8.2 Hz force bandwidth which is sufficient.