Abstract: Numerous studies have explored ways to introduce additives or conjugating materials into asphalt mixture to reduce dependency on petroleum-based asphalt. However, research on investigating the potential of locally accessible materials to substitute conventional petroleum-based asphalt and assessment of its prospective mixture with recycled materials is limited. Buton asphalt (Asbuton)-an abundant local resource in Indonesia, has several advantages over petroleum extracted asphalt due to its natural occurrence, high resistance and flexibility. Exposure to sunlight and rain-dominant climate characteristics in tropical region, makes this material stronger and denser with the texture becoming flexible and thus it reduces the possibility of cracks to develop. Plastic wastes, with only a few such as Polyethylene Terephthalate (PET) that is utilized as a mixture for pavement are ideal candidates as a conjugating material for asphalt mixture. Therefore, this research aimed to assess the potential of utilizing PET as a conjugating asphalt mixture by investigating the effect of mixing plastic wastes into Asbuton Buton Rock Asphalt (BRA)-a manufactured Asbuton version-in asphalt concrete layer (Laston) using Marshall characteristics as performance indicators. The laboratory testing results demonstrated that adding of the BRA and plastic waste flakes mixture into the AC-WC concrete mixture saved 8% of weight with an optimum asphalt content of 6.5%. Using the mixture of liquid Asbuton with BRA and 6% PET plastic flakes was able to improve the stability performance of asphalt mixture. The mixture characteristics, i.e., the stability, Marshal Quotient (MQ) and VFB increased while the flow, VIM and VMA reduced with the increasing rate of effective asphalt contents due to the addition of plastic waste flakes content. Furthermore, the residual Marshall stability obtained was above 90% and the voids at refusal densities were in the range of <2%. It is concluded that the PET and local non-oil-based composite asphalt mixture exhibits structural advantages and therefore can be considered sustainable for road pavement in tropical areas.