Abstract: A baby bottle assembly for bottom venting includes a bottle having a top closure member adapted for releasable engagement with a top portion of the bottle, and a bottom closure member adapted for releasable engagement with a base portion of the bottle. The bottom closure member has a base panel with a raised portion having an air passage therethrough and a top sealing surface. A diaphragm is positionable between the bottom closure member and the base portion. The diaphragm has a disc, at least one moveable sealing element for sealingly engaging the top sealing surface, and an air passage extending under the at least one moveable sealing element into the liquid chamber. The diaphragm is moveable between a sealed position and an unsealed position. The moveable sealing element when in the sealed position prevents liquid contained within a liquid chamber of the bottle from entering the air passage. When in the unsealed position, the diaphragm allows bottom venting of the bottle.