An inner module with a retainer is installed primarily inside a wireless earphone, including a circuit loop, an insulation seat to fix the circuit loop, and at least a retainer. The circuit loop includes at least a first circuit board, and at least a second circuit board which is extended from the first circuit board. The insulation seat includes at least a base plate to enclose the first circuit board, and a first side wall which is extended from the base plate. The first side wall is provided with a first positioning slot to accommodate the second circuit board. The retainer is fixed on the first side wall to fix the second circuit board in the first positioning slot. Therefore, the inner module is formed into a modularized design to simplify the assembly procedure of the wireless earphone.