Lignin have been blended with low density polyethylene (LDPE). Maleic anhydride grafted high density polyethylene (HDPE-g-MAH) has been added as compatibilizing agent. The weight ratio of LDPE, ligin and HDPE-a-MAH were 75:25:7.5, 75:25:10 and 75:25:12.5, respectively. The mechanical properties of the blends were investigated according to Chinese standard GB/1447-2005 and compared with those of lignin/LDPE composites without compatibilizing agent. Scanning electron microscopy (SEM) was used to investigate the dispersion of the lignin and LDPE and the compatibilizing mechanism was analyzed. The results reveal that addition of compatibilizing agent increased the interfacial bonding strength of the composites, improved the mechanical properties and obtained the better dispersion of the lignin and LDPE.