Coordinated planning for an integrated energy system (IES) could promote its operational security and economics, implement complementation among various kinds of energy systems, and improve the overall energy utilization efficiency. Given this background, the optimal planning problem of an IES with natural gas and heating networks is addressed. First, the mathematical model of an IES based on multiple energy hubs (EHs) is established, with the line pack of the concerned natural gas network, the heat loss and timedelay of the concerned heating network considered. Then, the optimal coordinated planning problem of an IES is addressed and a mixed integer nonlinear programming model attained, with an objective of minimizing its overall cost including investment and operation ones, so as to achieve the optimal placements of EH devices and energy networks. The optimal coordinated planning model is next transformed into a mixed integer linear programming problem by applying the incremental method, and then solved by the commercial solver Yalmip/Gurobi. Finally, an IES with six EHs is employed to demonstrate the proposed coordinated planning method. It is shown by simulation results that it is necessary to consider the characteristics of natural gas and heating networks in the IES planning, and the presented method is feasible.