A ceiling lamp includes a light body and a heat dissipation shroud. The light body includes a base platform to mount an illuminant thereat and two retention panels spacedly and upwardly extended from the base platform. The heat dissipation shroud has a plurality of heat dissipation holes and two elongated openings formed on the surrounding wall to guide the retention panels. The heat dissipation shroud further includes a fastener provided at a top edge of each of the elongated openings for detachably fastening with the base platform. When the ceiling lamp is installed into a ceiling, the heat dissipation shroud is covered by a thermal insulation layer above the ceiling, the heat dissipation shroud separates the light body from the thermal insulation layer for prevent heat being blocked by the thermal insulation layer, so as to prevent the overheat of the light body.