A heterogeneous cluster system consisting of different types of workstations and communication links plays an important role in parallel computing. In many applications on the system, collective communication operations are commonly used as communication primitives. Thus, design of the efficient collective communication operations is the key to achieve high-performance parallel computing. But the heterogeneity of the system complicates the design. In this paper, we consider design of an efficient gather operation, one of the most important collective operations. We show that an optimal gather schedule is found in O(n^2k-1) time for the heterogeneous cluster system with n processors od k distinct types, and that a nearly optimal schedule is found in 0(n) time if k=2.