Lignin is an amorphous biopolymer that has both polar and nonpolar characteristics which has been proven able to chemically bond bitumen and polypropylene. However, the presence of polar bond in lignin is more dominant than the nonpolar one making it less effective to bond polypropylene. Thus, lignin is modified to reduce its polar hydroxyl group by synthetizing it with prepolyurethane otherwise known as polyurethanization. This modified lignin compatibility to bond bitumen and polypropylene is then studied and compared with lignin, such is the true purpose of this research. Experiment is done through several stages ranging from sample preparation, mixing, and characterization. Hot melt mixing method is used to mix bitumen, polypropylene, and modified lignin with mass ratio of 19:1 for bitumen and polypropylene, which are mixed in 80 rpm. Mixing is done at the temperature of 180 °C for 30 min with 0.3% total weight addition of modified lignin. Characterizations are done using FT‐IR and FESEM. Result shows that modified lignin has better compatibility compared to pure lignin.