A work stool includes a support whose one end has a cushion and an opposite end has a base. The base has a bottom provided with a plurality of casters. The support has a gas strut. A tray is mounted around the support and positioned between the cushion and the base. A connecting assembly has one end fixedly connected to the tray and has an opposite end connected to the gas strut so that a distance between the tray and the cushion is fixed and the tray is adjustable in terms of altitude by operating the gas strut.