A new method was developed to backcalculate pavement layer modulifrom pavement surface deflection, measured by an FWD, using geneticalgorithms, It was found that layer moduli can be accurately estimatedby backcalculation using this method, with surface deflectioncalculated by the theory of elasticity for layer structures asthe input condition. This method was also applied to data of asphaltand concrete pavements, measured by the FWD. The results showedthat backcalculated moduli could sometimes be estimated even inthe case where an appropriate solution could not be obtained byconventional backcalculation methods.