A foldable car seat includes a base frame having a driver securely mounted thereon, a sliding frame operably connected to the driver and slidably attached to the base frame and having an adapter securely attached to a free end of the sliding frame so that the base frame is able to move relative to the sliding and a back frame foldably connected to the base frame and consisting of a pair of lower support frames foldably connected to free ends of the base frame through a first folding device and a pair of upper support frames foldably connected to free ends of the pair of lower support frames through a second folding device. The pair of lower support frames is foldable relative to the base frame and the pair of upper support frames is foldable relative to the pair of lower support frames. A locking mechanism is provided to the sliding frame to limit movement extent of as well as to position location of the sliding frame relative to the base frame.