A simple method to predict the resistance of SES (Surface Effect Ship) operated in calm sea is presented in this paper for the use of initial design of SES. Total resistance of SES is broken down into individual components ; sidehull frictional drag, seal frictional drag, cushion pressure wave making drag, aerodynamic drag, appendage drag, residual drag and waterjet inlet drag. To estimate each component, results of model tests and theoretical calculation are utilized. Among them it is shown that the estimation of wetted area of sidehulls and seal and trim angle is of critical importance. Predicted resistance of 30 ton type SES experimental craft shows good agreement with that of full scale trials data. Further study will be necessary to refine the method, especially regarding the residual resistance component.