A liftable keyboard for a portable electronic device is provided. The portable electronic device includes a top cover and a base. The liftable keyboard includes at least one key unit, a membrane switch circuit layer and a micro pump. Each key unit includes a keycap and an elastomer. When a sensing element within the base of the portable electronic device senses that the top cover is close to the base, the micro pump is enabled to perform a gas-extracting action. Consequently, the gas in the elastomeric chamber is extracted so that the elastomer is subjected to compressed deformation. The keycap is moved downwardly in response to the compressed deformation of the elastomer so as to reduce an altitude of the at least one key unit.