The present invention discloses an expandable keyboard device, including: a keyboard including a housing and a plurality of keys; a supporting assembly including a first panel and a second panel connected to said first panel, said second panel being adapted to connect with an electronic device, said supporting assembly being movable relative to said keyboard between an unfolded state and a folded state, said first panel upwardly supporting the electronic device relative to said keyboard when said supporting assembly is in said unfolded state so that the electronic device abuts against said keyboard and so that the display surface faces frontwardly, said supporting assembly and the electronic device covering said keyboard when said supporting assembly is in said folded state; a connetor which is inserted in the electronic device when the electronic device abuts against the keyboard; and a connecting unit interconnecting said supporting assembly and said housing, wherein said supporting assembly is movable relative to said keyboard through said connecting unit.