The biomedical applications of carbon nanotubes (CNTs) have been intensively investigated. However, poor water dispersibility and obvious toxicity of pristine CNTs are still two major issues for their biomedical applications. Although great efforts have been devoted to solving these problems, a simple and effective strategy for preparation of CNTs with high water dispersibility and desirable biocompatibility is still of great research interest. Herein, surface modification of CNTs with a biocompatible polymer polyethylene glycol (PEG) via a mussel inspired strategy has been developed. The dispersibility as well as biocompatibility of these PEGylated CNTs (named as CNT-poly(PEGMA-co-IA-DA)) was subsequently investigated. These PEGylated CNTs showed remarkable enhancement of dispersibility in aqueous and organic solvents. More importantly, as evidenced by cell viability and reactive oxygen species results, these PEGylated CNTs showed negative toxicity toward cancer cells. Therefore the PEGylated strategy described in this work can provide a general platform for fabrication of multifunctional biomaterials for various biomedical applications because of the advantages of mussel inspired chemistry and the excellent properties of PEGylated materials.