The invention relates to a miniature circuit breaker, which is characterized in that an operating mechanism and a static contact are arranged in a shell of the miniature circuit breaker, the operatingmechanism comprises a contact support, the contact support is provided with a moving contact matched with the static contact, and a shielding piece used for shielding electric arcs between the movingcontact and the static contact is arranged in the shell; the shielding piece is provided with a rotating end, a limiting end and a shielding end; the rotating end is rotatably connected with the shell, the limiting end is provided with a sliding groove used for controlling the relative positions of the shielding piece and the moving contact, and the moving contact extends into the sliding groovethrough the protruding contact part to drive the shielding piece to rotate around the rotating end relative to the moving contact; and during opening, the shielding end is rotated into the position between the moving contact and the static contact, and during closing, the shielding end is rotated out of the position between the moving contact and the static contact. In the opening and closing process, the shielding piece is driven by the moving contact under the action of the sliding groove and rotates around the rotating end relative to the moving contact, the structure is simple and compact,and the occupied rotating space is small.