The water-proof casing provides a waterproof casing for protecting an electronic device. It comprises a housing that has an internal space, at least an opening that is positioned on a surface of the housing, and a cover portion that covers the opening. As the material for making the housing is stretchable, the house may has only a single opening that is stretched to allow an electronic device to pass through. The housing may enclose an electronic device, which enters the housing through the single opening. A flexible material is used to make the opening that is stretched when the electronic device enters the housing. The opening includes a skirt that is pressed against a surface of the cover portion so that the water-proof function of the present disclosure may be achieved. The casing may include a tube unit to accommodate lens of the device.