A peripheral circuit disposed on a substrate having an active device array is provided. The peripheral circuit includes first test pads, second test pads, first lines, and second lines. The first and the second lines are electrically connected to the active device array. Each first test pad includes a first conductive layer and a second conductive layer electrically connected to the first conductive layer. The first conductive layer electrically connects at least two of the adjacent first lines. The second test pads are interposed between the first test pads and the active device array. Each second test pad includes third conductive layers and a fourth conductive layer electrically connected to the third conductive layers. The first lines pass through the third conductive layers and are insulated from the fourth conductive layer. Each third conductive layer is electrically connected to one of the adjacent second lines respectively.