A new method was developed to backcalculate pavement layer moduli from pavement surface deflection, measured by an FWD, using genetic algorithms, It was found that layer moduli can be accurately estimated by backcalculation using this method, with surface deflection calculated by the theory of elasticity for layer structures as the input condition. This method was also applied to data of asphalt and concrete pavements, measured by the FWD. The results showed that backcalculated moduli could sometimes be estimated even in the case where an appropriate solution could not be obtained by conventional backcalculation methods.