An electronic device case includes a first shell, a second shell, and a side button. The first and second shells are each provided with a peripheral side plate. A passage communicating the inside and outside of the case, a first restriction slot extending from the passage toward the first shell, and a second restriction slot extending from the passage toward the second shell are formed jointly by the peripheral side plates of the shells embedded with each other. The side button is provided with a base and a press portion protruding from the base. The thickness of the base is larger than or equal to the widths of the restriction slots. The side button is installed in the passage with the base embedded in the restriction slots. As a result, the case is sufficiently water resistant, firm in structure and easy to assemble.