PURPOSE: To produce a bundled fiber generating no opening of chips at the time of the forming of staple fiber chips by preliminarily bonding org. heat- resistant resin particles whose primary particles have an average particle of 100μm to a fiber bundle and subsequently applying bundling agent thereto.

CONSTITUTION: Org. heat-resistant resin particles whose primary particles have an average particle size of 100μm or less are bonded to a fiber bundle composed of reinforcing fiber such as a glass fiber, a carbon fiber, a ceramics fiber or a para-oriented aromatic polyamide fiber by a spray method. Subsequently, a bundling agent dissolved or dispersed in a solvent is applied to the fiber bundle having the org. heat-resistant resin particles bonded thereto to produce a bundled reinforcing fiber. This bundled reinforcing fiber is cut into a predetermined length to make it possible to obtain staple fiber chips. As a suitable example of an org. heat-resistant resin, there are aromatic polyamide, aromatic polyamideimide and aromatic polyimide.