To provide a printed wiring board wherein the base material of printed wiring board for build-up is improved for forming a high density circuit.

An inner layer and a build-up layer comprises a thermosetting resin composition layer of a nonwoven glass fiber whose thickness is 100 μm or less and which includes flat glass fibers by 90 wt.% or more that is rectangular in cross section, with its major diameter/minor diameter of 3.1/1-5/1, whose cross-section area is 90-98% of a rectangle circumscribing the cross section of glass fiber, with reduced fiber diameter 5-17 μm. Thus, a multilayer printed wiring board is provided which is excellent in surface smoothness and boring characteristics with a carbon dioxide laser as well as in connection reliability for the hole while suitable for forming a high density circuit.