An underwater housing includes a housing body for containing an electronic device, a seal cap for sealing a rear end opening of the housing body, and a spacer member for dividing a space between the housing body and the seal cap into a cable chamber and an accommodating chamber. The seal cap includes an annular front cap element connected fixedly and sealingly to the housing body, and a rear cap element disposed fixedly and fittingly within the rear end of the front cap element. The rear cap element has a hole permitting an electrical cable to sealingly extend therethrough. The spacer member includes a spacer body disposed sealingly in said seal cap, and a plurality of conductive terminals extending sealingly through the spacer body and interconnecting electrically the electronic device and the electrical cable.