A compressible device for use on a drinking container includes a base and at least one spill-proof unit. The base includes a base wall defining a liquid flow passage, and a separation wall connected to the base wall and dividing the liquid flow passage into a liquid inlet zone and a liquid outlet zone. The at least one spill-proof unit includes a through slot formed in the separation wall and communicating with the liquid outlet zone, and a spill-proof seat including a plate body opposite to the through slot and formed with a first slit. When the plate body is compressed and deformed, the first slit is opened to communicate the liquid inlet zone with the liquid outlet zone through the through slot.
