To provide a method for easily fixing extrafine fibers onto a substrate while keeping their pores, in the case of needing fixing e.g. a nonwoven fabric comprising such extrafine fibers onto a film, woven fabric or the like, for example, in the case of artificial blood vessels which have enough flexibility and mechanical strength to withstand blood pressure and/or stretch and contraction stemming from body motion and required such the function that substances therein can selectively permeate it.

The method for fixing an extrafine fiber layer on a substrate comprises heating the extrafine fibers each composed of a plurality of components to a temperature higher than the lowest melting point among those of the respective components to melt the component in question.