The blade-holder (3,4) for a harmonica according to the invention supporting at least one vibrating tonal blade (301, 401) comprises air-tightness means formed by side walls (301 L, 401 L) and an end wall (301 E, 401 E) extending in the continuation of the side faces and of the corresponding end face of the window through which the free part of the tonal blade concerned (301, 401) oscillates.