A positioning device for a polarization plate is disposed adjacent to a transferring roller for receiving the polarization plate transferred from the transferring roller and further roughly positioning the polarization plate. The positioning device includes a positioning platform, a driving mechanism; and a conveying mechanism located under the positioning platform and connected to the driving mechanism. The conveying mechanism is capable of being driven to move upwards relative to the positioning platform by the driving mechanism to be partly exposed above the positioning platform. The positioning device ensures that the whole polarization plate can enter the positioning platform from the transferring roller and be transferred to the target position.