A scheme for teleporting an unknown two twolevel atoms entangled state via four identical twolevel atoms nonmaximally entangled Cluster state as quantum channel is proposed. In the scheme, the receiver Bob can reconstruct the original state with a certain probability by introducing an auxiliary atom and operating unitary transformations according to the sender Alice′s measurement results, and the successful probability is determined by the smallest two coefficients′ absolute values of the Cluster state. The considerable advantage of the scheme is that a nonmaximally entangled Cluster state is employed as quantum channel, thus, the scheme can greatly reduce the amount of entanglement resources and need less classical bits. If a maximally entangled Cluster state is employed as quantum channel, the probabilistic teleportation scheme becomes usual teleportation, of which the successful probability is 100%.