The invention relates to a kind of volumetric pipet. It includes an outer casing. At the lower part of the outer casing, there is a fetching mouth which is detachably mounted to a liquid container. At the top of the outer casing, there is a detachably sealed top cover. Inside the outer casing, there is a hollow core with a top opening. There is an inlet mouth on the side wall of the core that corresponds to the fetching mouth. The internal wall of the outer casing can slide against the external wall of the core. The core's rotating or sliding along its longitudinal orientation makes the fetching mouth and the inlet mouth correspond or stagger. This invention provides an easy-to-operate, precise rationing, quick and sanitary volumetric pipet.