A blade for a gas turbine includes an external structure including a plurality of seating grooves which are separately disposed in a chord direction toward a trailing edge from a leading edge, an internal structure received in the external structure and including a plurality of protrusions protruding toward an internal side of the external structure, a plurality of porous strips combined to the seating groove in an attachable/detachable way, and a coolant channel formed for a coolant to flow among the porous strip, the neighboring protrusions, and an external side of the internal structure.