In the past 20 years, in view of (QDs) of special properties, especially the QDs relative to the optical properties of organic dyes, easy adjustment and photo-degradation resistant properties, the QDs has been widespread concern [1]. It has been widely explored as light-emitting devices (LEDs), lasers, sensors, solar cells and biomedical labeling [2, 3]. In this paper, highly photoluminescent Graphene quantum dots (GQDs) have been prepared via simple one-step method. They were characterized by X-ray powder diffraction (XRD), photoluminescence (PL), UV-vis diffuses reflectance spectra (UV), transmission electron microscope (TEM) and scanning electron microscopy (SEM). The particle size of GQDs can be easily controlled, and these type of GQDs have tunable particle size with the average diameter of 5-7 nm. These GQDs show strong and stable photoluminescence which is dependent on excitation wavelength. It is to be noted that the GQDs can efficiently were taken up by liver cancer cells HepG2. Additionally, due to its high photostability and biocompatibility, the obtained carbon dots are demonstrated as excellent probes in cellular imaging.