Plastic waste such as HDPE and PET is a serious environmental problem in Indonesia because it is difficult to decompose naturally. This study aims to analyze the tensile strength and macrostructure of composites between HDPE, PET, and dried coconut fiber plastic waste with a polyester resin matrix. Six composition variations were tested using the ASTM D638 Type IV standard, with tensile and macro tests. The test results showed that the composite with 50% coconut fiber provided the highest tensile strength with an average of 794.4 N and an average stress of 26.47 MPa, while the composite with 50% HDPE had the lowest tensile strength with an average of 242.7 N and an average tensile stress of 8.09 MPa. The macrostructure of all specimens appeared dense and homogeneous. Voids were only found in specimens containing coconut fiber, but did not significantly affect the tensile strength value because they originated from natural fiber fractures, not production defects. Thus, coconut fiber is proven to be an effective and environmentally friendly natural reinforcing material, and is able to improve the mechanical properties of plastic waste-based composites.