A method of preparing window glass provided with a gasket at a peripheral portion of a glass sheet for a window includes placing a glass sheet in a shaping mold which has two mold parts to provide an inner cavity in which resilient sealing members are attached respectively to the two mold parts so as to come in contact with surfaces of the glass sheet so that a gasket forming cavity is formed at a peripheral area of the glass sheet by the cooperation of the inner cavity of the shaping mold, the resilient sealing members and the glass sheet. The resilient sealing member is then pushed to the contacting surface constituted by the resilient sealing member and a part of the shaping mold in the inner cavity via a pushing means after the assembling of the shaping mold and the glass sheet. A gasket material is then injected into the gasket forming cavity to form a gasket.