We present a scheme for probabilistic teleportation via a non-maximally entangled GHZ state.Quantum teleportation will succeed with a calculable probability.The teleportation process requires the sender to make a generalized Bell state measurement,the cooperator to perform a generalized X basis measurement,and the receiver to perform a collective unitary transformation and to make a measurement on an auxiliary particle.The success probability of the teleportation is given.We also obtain the maximum of the s...