A fold-down tablet used in a chair is disclosed. The tablet includes a board, a torsion positioning mechanism, a shaft and an armrest. The torsion positioning mechanism is fixed to a side of the board for horizontally rotating and positioning the board. The shaft has a protrudent positioning bar and is fixed to the torsion positioning mechanism for making the board vertically rotatable. The armrest has a shaft hole for rotatably receiving the shaft and a slot communicating with the shaft hole. When the board is turned horizontally, the positioning bar is embedded into the slot to be restricted.