Abstract: In order to study the flexural toughness and damping characteristics of recycled polyethylene terephthalate (PET) plastic aggregate mortar (RPAM), the recycled PET plastic aggregate (RPA) was prepared from the wasted PET plastics. Taking RPA substitution rate as the variable, the three-point bending loading test and the suspension beam bending free vibration test on RPAM were carried out. The load-deflection curve, flexural toughness, first-order damping ratio and frequency of RPAM with different RPA substitution rates were analyzed. Besides, the damping mechanism of RPA interface was analyzed based on the SEM test. The results show that with the increase of RPA substitution rate, the ductility of RPAM increases, the slopes of loading branch and unloading branch of load-deflection curve gradually decrease, and the initial crack strength and flexural strength decrease. The addition of RPA makes the failure of RPAM more ductile, which increases the initial crack deflection and peak deflection significantly. The toughness indexes I₅, I₁₀ and I₂₀ are 4.17, 5.65 and 5.89 times larger than that of ordinary mortar, respectively. The residual strength of RPAM increases gradually as the RPA substitution rate increasing. With the increase of RPA substitution rate, the first-order frequency of RPAM decreases by 9.0%-25.9%, while the damping ratio increases by 11.3%-58.1%. The micro structure of interface transition zone (ITZ) between RPA and cement matrix is loose. The slippage and friction of the ITZ and the viscosity of RPA increase the damping energy consumption of RPAM, and the recommended dosage of RPA is in the range of 15.5vol%-17.2vol%.