Conventional glass-based pH sensors are usually fragile and space consuming. Herein, a miniature electrochemical pH sensor based on amino-functionalized graphene fragments and polyaniline (NH2-G/PANI) composite film is developed via simply one-pot electrochemical polymerization on the ITO-coated glass substrates. Cyclic Voltammetry (CV), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and Raman Spectra are involved to confirm the successful synthesis and to characterize the properties of the NH2-G/PANI composite film. The developed electrochemical pH sensor presents fast response, high sensitivity (51.1 mV/pH) and wide detection range when applied to PBS solutions of pH values from 1 to 11. The robust reproducibility and good stability of the developed pH sensors are investigated as well. Compared to the conventional glass-based pH meters, the NH2-G/PANI composite film-based pH sensor could be a promising contender for the flexible and miniaturized pH-sensing devices.