A polyimide (PI) having two —COOH capping groups at each end is provided. A coating composition is further provided, which contains the PI and a hardening agent having 2 to 6 functional groups capable of reacting with —COOH. A PI coating layer and PI film formed by the coating composition of the present invention possess excellent chemical resistance and coefficient of thermal expansion (CTE), which makes them applicable in fabrication of protective materials for active/passive devices, optical materials, touch panels, copper foil substrates, soft flexible electronic materials or integrated circuit elements, or film substrate for glass film touch panels.