A substrate processing system and substrate transferring method is capable of improving substrate-transferring efficiency by transferring a substrate bi-directionally through a substrate transferring device between two rows of processing chambers, and transferring the substrate to a precise position by rotating the substrate transferring device. The processing system includes a transfer chamber, a bi-directional substrate transferring device; and processing chambers which apply a semiconductor-manufacturing process to the substrate. The processing chambers are linearly arranged along two confronting rows, and the transfer chamber is between the two rows of processing chambers. The substrate transferring device includes a moving unit inside the transfer chamber; a bi-directional substrate transferring unit in the moving unit, that transfers the substrate to the processing chamber through a bi-directional sliding movement; and a rotating unit between the moving unit and the bi-directional substrate transferring unit, that rotates the bi-directional substrate transferring unit at a predetermined angle.