A compensating chuck for concentrically clamping workpieces. The chuck has a drive unit having two pairs of entrainment members, wherein the entrainment members are preferably slidingly mounted, are respectively movable in paired relationship, and are so coupled to a respective one of the main jaws that a relative movement of a respective pair causes a synchronous movement of adjacent main jaws and that both a relative movement relative to each other with respectively different movement components and also a synchronous movement of the adjacent entrainment members in the same direction respectively causes a relative movement of adjacent main jaws.

A chuck assembly includes a chuck having a cross-shaped installation hole defined therethrough. A toothed disk is connected to the chuck and exposed from the outer periphery of the chuck. A driving unit includes a shaft and a gear which is mounted to the shaft. The driving unit is installed in the installation hole. The shaft includes two threaded sections respectively formed on two ends thereof. Two pawls each have threaded hole which is threadedly connected to the threaded section of the shaft corresponding thereto. When the gear is rotated to rotate the shaft, the two threaded sections are rotated to move the two pawls to move toward each other or away from each other.