A plurality of tubes and corrugated fins are piled up and arranged alternatively, for integrally assembled heat exchangers. The corrugated fin has fin portions for the heat exchangers and a connecting portion connecting the fin portions. The connecting portion is formed with slits arranged in first and second lines extending in a longitudinal direction of the fin and at least one louver between the slits in the lines. The slits in the first line and the slits in the second line traverse a top portion and a bottom portion adjacent to the top portion of the fin and the louver is formed on an intermediate portion between the top portion and the bottom portion so that the louver is located between the space of the slits in the first line and the space of the slits in the second line.