Poly(butylene succinate) (PBS)/polylactic acid (PLA) blends modified with dicumyl peroxide (DCP) werereinforced by PBS-g-cellulose nanocrystal (CNC) through melt mixing. PBS-g-CNC was prepared throughin situ polymerization and its structure was confirmed by FTIR,13C NMR, XPS and GPC analysis aftersaponification. The morphological analysis of PBS/PLA/PBS-g-CNC composites before and after etched byCH2Cl2shows that the addition of DCP and PBS-g-CNC could decrease the size of PBS as a dispersed phasein PLA matrix and improve the dispersion of PBS-g-CNC in both PBS and PLA phases, which could affectthe crystallization and mechanical properties of composites. The crystallinity of PLA -phase crystalin PBS/PLA/PBS-g-CNC composites is increased obviously by the addition of PBS-g-CNC, leading to anincrease of the crystallinity of the composites. PBS/PLA blends modified by DCP have high Notched Izodimpact strength and moduli, and the values are increased by the addition of PBS-g-CNC. Both storagemodulus and glass translation temperature of PBS/PLA blend are increased by DCP and PBS-g-CNC, whichis proved by DMA results, showing a weak molecular segment mobility of PBS/PLA matrix. The additionof DCP decreases the crystallization temperature and crystallinity of PBS/PLA composite, but increasesthe thermal stability of composites, mostly because of the crosslink effect of DCP on PBS/PLA matrix