A casing assembly for electronic device, comprising: a first casing; a second casing; and a hinge assembly (30, 30a, 30b, 30c), comprising: a fixed frame (31, 31c), fixed to the first casing; a shaft, rotatably disposed on the fixed frame (31, 31c); a rotatable frame, fixed to the shaft and the second casing, wherein the rotatable frame has a first positioning structure, the rotatable frame comprises a base and two rotatable components, the base is fixed to the shaft, the two rotatable components are rotatably disposed on the base and fixed to the second casing, and a rotation axis of the two rotatable components relative to the base is perpendicular to a rotation axis of the base relative to the fixed frame via the shaft; and a cover (34, 34a, 34b, 34c), fixed to the first casing; wherein the fixed frame or the cover (34, 34a, 34b) has at least one second positioning structure (311c, 3411, 3411b, 3421a), and the first positioning structure and the at least one second positioning structure (311c, 3411, 3411b, 3421a) are cooperated with each other so as to limit a rotatable range of the base of the rotatable frame relative to the fixed frame via the shaft; characterized in that the cover (34, 34a, 34b, 34c) comprises a horizontal plate (341, 3411a, 341b) and a vertical plate (342, 3412a, 342b), the vertical plate (342, 3412a, 342b) stands on the horizontal plate (341, 3411a, 341b), the horizontal plate (341, 3411a, 341b) has a sleeve hole, an opening of the sleeve hole is located at one side of the horizontal plate (341, 3411a, 341b) located opposite to the vertical plate (342, 3412a, 342b), the horizontal plate (341, 3411a, 341b) is located between the rotatable frame and the fixed frame (31, 31c) and is sleeved on the shaft through the sleeve hole. a first casing; a second casing; and a hinge assembly (30, 30a, 30b, 30c), comprising: a fixed frame (31, 31c), fixed to the first casing; a shaft, rotatably disposed on the fixed frame (31, 31c); a rotatable frame, fixed to the shaft and the second casing, wherein the rotatable frame has a first positioning structure, the rotatable frame comprises a base and two rotatable components, the base is fixed to the shaft, the two rotatable components are rotatably disposed on the base and fixed to the second casing, and a rotation axis of the two rotatable components relative to the base is perpendicular to a rotation axis of the base relative to the fixed frame via the shaft; and a cover (34, 34a, 34b, 34c), fixed to the first casing; wherein the fixed frame or the cover (34, 34a, 34b) has at least one second positioning structure (311c, 3411, 3411b, 3421a), and the first positioning structure and the at least one second positioning structure (311c, 3411, 3411b, 3421a) are cooperated with each other so as to limit a rotatable range of the base of the rotatable frame relative to the fixed frame via the shaft; a fixed frame (31, 31c), fixed to the first casing; a shaft, rotatably disposed on the fixed frame (31, 31c); a rotatable frame, fixed to the shaft and the second casing, wherein the rotatable frame has a first positioning structure, the rotatable frame comprises a base and two rotatable components, the base is fixed to the shaft, the two rotatable components are rotatably disposed on the base and fixed to the second casing, and a rotation axis of the two rotatable components relative to the base is perpendicular to a rotation axis of the base relative to the fixed frame via the shaft; and a cover (34, 34a, 34b, 34c), fixed to the first casing; wherein the fixed frame or the cover (34, 34a, 34b) has at least one second positioning structure (311c, 3411, 3411b, 3421a), and the first positioning structure and the at least one second positioning structure (311c, 3411, 3411b, 3421a) are cooperated with each other so as to limit a rotatable range of the base of the rotatable frame relative to the fixed frame via the shaft; characterized in that the cover (34, 34a, 34b, 34c) comprises a horizontal plate (341, 3411a, 341b) and a vertical plate (342, 3412a, 342b), the vertical plate (342, 3412a, 342b) stands on the horizontal plate (341, 3411a, 341b), the horizontal plate (341, 3411a, 341b) has a sleeve hole, an opening of the sleeve hole is located at one side of the horizontal plate (341, 3411a, 341b) located opposite to the vertical plate (342, 3412a, 342b), the horizontal plate (341, 3411a, 341b) is located between the rotatable frame and the fixed frame (31, 31c) and is sleeved on the shaft through the sleeve hole.