A core strip for a honeycomb core panel is composed of a metal strip shaped into a corrugated configuration and having continuous alternate convex and concave portions of identical shape, each of the convex portions being defined by a plateau portion and a pair of inclined portions, and each of the concave portions being defined by a bottom portion and the pair of inclined portions. The inclined portions interconnect the plateau portion and the bottom portion. At the one side edge of the shaped metal strip, the plateau portion and the inclined portions have respective first flanges disposed perpendicular to the metal strip and directed away from a convex surface of the convex portion. At the other side edge of the shaped metal strip, the bottom portion and the inclined portion have respective second flanges disposed perpendicularly to the metal strip and directed away from a convex surface of the concave portion. With this construction of the core strip, the core strips can be welded together with high uniformity and high weldability, and the thickness of the core strip can be greater than that of a conventional one. In the formation of a honeycomb core panel, such core strips can facilitate the bonding between a core and face sheets, and also enable a stable bonding.