Abstract: Disclosed is a precision rotational transmission mechanism, comprising a fixing support (1), wherein the fixing support (1) is provided with a rotational case (112), which is connected to an electric motor and is provided with a first transmission mechanism (1122), a second transmission mechanism (33) and an output member (19) therein, an end of the first transmission mechanism is connected to the electric motor, the other end is connected to the second transmission mechanism, and the second transmission mechanism drives the rotational case to rotate simultaneously via the output member. The transmission mechanism has a simple and compact structure, has a larger output shaft which has bigger rigidity and can output from two ends, has a lighter overall weight which is suitable for industrialization and mass production, has a large transmission ratio, high transmission efficiency, small return difference, strong carrying capacity, strong impact resistance capacity, and long service life.