As amphiphilic substances, graphene oxide sheets (GOSs) can be used as surfactants in numerous technological fields. Wherein, utilizing GOSs to compatibilize immiscible polymer blends constitutes a promising direction because it not only harnesses their amphiphilic character but also exploits their extraordinary properties. Here, we show that polymer functionalization of GOSs can greatly expand their compatibilizing range. For example, commercially important polyolefin-based polymer blends, which are beyond the compatibilizing scope of unmodified GOSs, can be compatibilized by polypropylene-grafted GOSs (PP-g-GOSs). With the incorporation of 0.5 wt% of PP-g-GOSs into immiscible PP/polyphenylene oxide (PP/PPO, 90/10) blends, the dispersion of the minor phase (PPO) is remarkably improved without visible agglomerates. The compatibilizing effect of PP-g-GOSs should be due to the fact that they can adsorb PPO on their basal planes while exhibit intermolecular interactions with PP through their grafted PP chains. Moreover, PP-g-GOSs also act as multifunctional fillers for PP/PPO blends, thus enhancing their flame retardancy, thermal stability, mechanical strength and nucleation ability. The PP-g-GOS-compatibilized PP/PPO blends achieve an excellent combination of good melt processability and low cost of PP with multifunctional performances of PPO and GOSs, thereby holding enormous potential in many fields.