To obtain a composite fiber apart from agglomeration and entanglement and allowing solid particles on the surface of the fiber to fulfill its function sufficiently independently of the kind of the fiber by specifying the length and the axial ratio of the fiber and fixing the solid particles onto the surface of the fiber by an impingement method using a high-speed air stream.

This method for producing a composite fiber is to fix solid particles with a mean particle size of 0.1 to 100 μm onto the surface of a fiber with a weight average fiber length of 0.1 to 5 mm and axial ratio of 5 to 300 by an impingement method using a high-speed air stream in a dry manner. The usable fiber is not limited to a sort of hydrophilic fiber, and the resultant composite fiber needs no dry process, bears the solid particles on the surface thereof in high ratio, and is useful for production of e.g. a thin film with high opacity.