An inspection apparatus for a TFT substrate formed with a plurality of pixels, includes a reference substrate being opposite to and spaced from the TFT substrate and formed with a plurality of reference patterns corresponding to the pixels, a power supply to supply power to both a predetermined number of the pixels and the corresponding reference pattern to form an electric field in a space between the TFT substrate and the reference substrate, an electron beam emitter to emit an electron beam to travel from a first side to a second side of the space, an electron beam detector to detect the electron beam emitted from the electron beam emitter and passed through the space, and a controller to determine whether the TFT substrate includes a defective pixel based on a location of the electron beam detected by the electron beam detector. Thus, the inspection apparatus can correctly and quickly inspect the TFT substrate for defects in a low vacuum state regardless a size of the TFT substrate.