Poly(vinyl alcohol) (PVA) functionalized graphene (f-G) was prepared by ultrasonication of pristine graphene (p-G) in a PVA aqueous solution. PVA macroradicals formed by sonochemical degradation of the PVA solution were successfully trapped by graphene and grafted onto its surface. This was confirmed by transmission electron microscopy, atomic-force microscopy and ¹H NMR measurements. The content of PVA on graphene was estimated to be 35%. The f-G could be well dispersed in the PVA matrix by a simple solution mixing and casting procedure. Due to the effective load transfer between f-G and PVA matrix, the mechanical properties of the f-G/PVA films were significantly improved. Compared with the p-G/PVA films, a 12.6% increase in tensile strength and a 15.6% improvement of Young's modulus were achieved by addition of only 0.3 wt% f-G. Moreover, our simple ultrasonication technique could enable us to functionalize graphene with other polymers.