Abstract: A stage cementing tool comprising a substantially tubular mandrel having a single interior unitary sleeve maintained at a first or closed position in said mandrel and adapted to move to a second or open position and subsequently to a third or closed position in said mandrel. The movable unitary sleeve is maintained by interior shear pins adapted to be sheared in two steps by separate forces applied at different points of the assembly of the unitary sleeve and respective opening and closing seats secured thereto. Positive locking means are located in the sleeve which act to maintain it at each successive position and to prevent regression when the moving force is removed. The mandrel and assembly is adapted to fit in a string of casing pipe for location at a site to be cemented. In operation the unitary sleeve is first actuated to open position for cement flow and placing and thereafter to fully closed position to stop such flow and is positively locked in such closed condition.