Successful use of synthetic lightweight aggregates made from waste fly ash and plastics can help in conserving mineral aggregates and reusing waste materials. The objective of this study was to evaluate the use of synthetic lightweight aggregate made from waste fly ash and plastics in hot-mix asphalt. The scope of this laboratory study included preparation of aggregate blends and mixes with different percentages of synthetic lightweight aggregates, compaction of samples, testing of samples, and analysis of results. Mixes were made with 0%, 5%, 10%, 15%, and 20% synthetic lightweight aggregates by weight of aggregates. Tests included bulk specific gravity, theoretical maximum density, resilient modulus, and indirect tensile strength at 25 deg C on unconditioned and conditioned samples as well as rut testing with wheel tracking equipment at 60 deg C. Test results were analyzed statistically to determine the effect of synthetic lightweight aggregates on hot-mix asphalt properties. The results indicate that the inclusion of synthetic lightweight aggregates enhances stiffness and resistance against rutting and moisture-induced damage of hot-mix asphalt. A relatively high absorption was noted for mixes containing 20% synthetic lightweight aggregates. The main conclusions are that synthetic lightweight aggregate has excellent potential for being used as part of hot-mix asphalt, and 15% by weight of aggregate appears to be an optimum amount for use. Further work should be pursued to determine the effect of synthetic lightweight aggregate on low-temperature properties of hot-mix asphalt.