A reinforcing fiber base for composite materials, having at least two layers of unidirectional reinforcing fiber bundles and being characterized in that the directions of the fiber bundles in each of the layers are different between the adjacent layers and that a thermoplastic resin component adheres at random and partially to the surface of the fiber bundle of at least one of the fiber bundle layers such that the bundle layers are bonded to each other by means of the thermoplastic resin component. The base can be well impregnated with a matrix resin, is excellent in mechanical characteristics, and has a good shapability.
