To produce a high-quality and long-lasting pavement, quality assurance (QA) is critical. For flexible pavements, layer thickness and in-situ density are the two most important characteristics to monitor. This paper presents the successful application of ground penetrating radar (GPR) to nondestructively and continuously measure asphaltic layer thickness and density. Ground penetrating radar surveys were conducted at a five-lane full-scale test site. Each lane is composed of four sections with the same asphaltic mixture but different densities. The GPR signal reflection was used to predict the layer thickness profile. Specific gravity models developed in an earlier study were utilized to predict the asphalt mixture density profile. The GPR-predicted thickness and density were compared to the core-measured values. Results showed that GPR achieved an average relative error of 4.9% in layer thickness measurement without using calibration cores and an average relative error of 2.6% in asphalt mixture bulk specific gravity using one calibration core.