A study on dynamic backcalculation and overlay design based on falling weight deflectometer (FWD) data is presented. Dynamic slab-ground theory (DSGT) was used for dynamic backcalculation of a pavement structure. A computer program based on DSGT generated theoretical dynamic deflections of the pavement. For the backcalculation of equivalent full-depth asphalt concrete (AC) thickness and subgrade modulus, these deflections were matched with FWD deflections from major roads in Miyazaki Prefecture, Japan. Temperature influence on Young's modulus of AC was also considered. Results were then compared with those from DSGT's static analysis version (SSGT) and also from a Japanese representative method, NIPPO, which is a static elastic multilayer method. Characteristics of dynamic backcalculation analysis are discussed. The range of pavement variables showing necessity for dynamic analysis was also considered by comparison of theoretical deflections using DSGT and SSGT. Furthermore, overlay thickness design using Kentucky Transportation Center's procedure was carried out.