Reactive compatibilization is a cost-effective and efficient way to fabricate high-performance multicomponent polymeric materials. The reactive compatibilization of low-density polyethylene (LDPE) and poly(L-lactide) (PLLA) blends has seldom been reported because LDPE is inert to the chemical reaction during melt compounding. In this work, we first grafted carboxylic acid groups onto the PE molecular chains (m-LDPE), followed by a facile binary grafting strategy to compatibilize PLLA/LDPE blends. Poly(styrene-co-glycidyl methacrylate) (SG) has been used as the main chains for the binary grafting. The carboxylic acid groups of both PLLA and m-LDPE can react with the epoxide groups on SG main chains during the melt blending, leading to the in situ formation of both LDPE and PLLA grafted copolymers. Such binary grafted copolymers act as effective compatibilizers for the highly immiscible PLLA/LDPE (80/20) blends. The compatibilized blends exhibit excellent mechanical performance. The tensile strength of the compatibilized PLLA/LDPE blends increases from 26.4 to 36.7 MPa, and the elongation remarkably enhances from 9 to 367%, as compared with the same blends without compatibilization. At the same time, the Charpy impact strength of the compatibilized blend is 100.1 kJ/m(2), which is 6.2 times that of the LDPE/PLLA binary blend. The fabricated PLLA/LDPE blends show potential engineering applications as environment-friendly materials. In addition, the in situ binary grafting strategy paves a new possibility for the reactive compatibilization of immiscible polymer blends with no reactive groups.