Provided is a substrate treating apparatus using a process gas and an adjustment plate used thereof. A substrate treating apparatus including a chamber providing a space in which a process is performed, a support member supporting a substrate in the chamber, a gas supply member supplying a process gas onto the substrate disposed on the support member, and an exhaust assembly coupled to the chamber to exhaust a gas in the chamber, wherein the exhaust assembly includes an exhaust pipe connected to the chamber, an exhaust member connected to the exhaust pipe to provide a vacuum pressure in the exhaust pipe, a valve adjusting an opening rate of the exhaust pipe, and an adjustment plate having a cover plate which is provided in the chamber to interfere with a flow of the process gas in an internal region of the chamber in a direction corresponding to, when the exhaust pipe is partially opened, an opened region of the exhaust pipe. Consequently, the process gas may be uniformly supplied onto the substrate.