Abstract: The term present serviceability was adopted to represent the momentary ability of pavement to serve traffic and the performance of the pavement was represented by its serviceability history in conjunction with its load application history. Serviceability was found to be influenced by longitudinal and transverse profile as well as the extent of cracking and patching. The amount of weight to assign to each element in the determination of the over-all serviceability is a matter of subjective opinion. In the present study, a regression tree model has been presented for determining flexible pavement surface layer thickness. The model, RT was selected as estimating method. Results show that wearing course thickness of flexible pavement regression values of the regression tree model is better than that of the AASHO model. This approach can be easily and realistically performed to solve the optimization problems which do not have a formulation or function about the solution.