The invention relates to a miniature circuit breaker. The technical problems that an operating mechanism of an existing miniature circuit breaker is poor in precision, low in stability and poor in using performance when used are mainly solved. The miniature circuit breaker comprises an outer shell, a contact support, a moving contact, a lock catch and a tripping buckle. The lock catch is matched with the tripping buckle, a first locating plate and a second locating plate which are spaced by a certain gap are arranged on the contact support, protruding rings are arranged on the outer side of the first locating plate and the outer side of the second locating plate, double torsional springs are arranged on the contact support and comprise a first torsional spring and a second torsional spring, the first torsional spring and the second torsional spring are symmetrically distributed on the two sides of the moving contact, the protruding rings of the locating plates are sleeved with the first torsional spring and the second torsional spring respectively, one end of the first torsional spring and one end of the torsional spring are respectively in clamping fit with the contact support, the other end of the first torsional spring and the other end of the second torsional spring are connected and are respectively in clamping fit with the moving contact, the first locating plate, the second locating plate and the protruding rings are provided with a fixed shaft, and the moving contact is arranged in a clearance and is hinged to the fixed shaft. Due to the fact that the miniature circuit breaker is reasonable in structural design, locating is accurate, high stability and good use performance are achieved, and in addition, the miniature circuit breaker has the advantages of being simple in structure, low in cost, convenient to mount and the like.