A folding device of a wheelchair includes a first folding unit and a second folding unit, wherein the first folding unit includes a first part, a second part and a connection rod connected between the first part and the second part. The first part has a first link and a second link respectively and pivotably connected thereto, and the second part has a third link and a fourth link respectively and pivotably connected thereto. The second folding unit has two boards and the two boards have two connection units. Each board has a recess and two lugs. Each recess has a first plate and a second plate connected thereto. A handle has two ends which are respectively and pivotably connected to the first and second plates.