Patented is a heat-resistant synthetic fiber sheet comprising, as principal components, a plurality of staple fibers. Also included is a heat-resistant organic synthetic polymeric material and a binding member selected from the group consisting of heat resistant organic synthetic polymer fibrids and mixtures of the heat resistant organic synthetic polymer fibrids with organic resin binders. The plurality of staple fibers are bound to each other through the binding member to form a paper-like sheet. The content of the staple fibers is in the range of 40-97% by mass on the basis of the total mass of the sheet. The total content of the binding member is in a range of from 3 to 60% by mass on the basis of the total mass of the sheet. At least a portion of the staple fibers has two flat end faces at an angle of 10 degrees or more to a plane crossing the fiber axis of the staple fiber at right angles.