An overvoltage and undervoltage tripper of a small-sized breaker solves the problem of complicated structure of an existing tripper and comprises a casing. The casing is provided with a control circuit board and a tripping driver inside. The tripping driver comprises a coil former, a movable iron core, a fixed iron core and an ejector rod, a rotation part is sleeved inside the casing, the ejector rod corresponds to the rotation part, the rotation part is provided with a connecting shaft, the connecting shaft penetrating through an arc groove on the casing to be connected with a lock catch of the breaker, the casing is provided with a guide mechanism, and the guide mechanism is matched with the rotation part. The overvoltage and undervoltage tripper of the small-sized breaker has the advantages that the motion manner of rotation of the single rotation part is created, tripping of the breaker is realized, transmission mechanism of an original tripper is simplified, size of the tripper can be reduced indirectly, assembling difficulty is reduced, and labor is saved. Furthermore, the lock catch can move in a unique and accurate track by the aid of the guide mechanism arranged on the casing.