a method for producing a fuel cell unit including a membrane electrode assembly formed by a solid polymer electrolyte membrane and a pair of electrodes located at both sides of the solid polymer electrolyte membrane , and a pair of separators which hold the membrane electrode assembly . the method includes the steps of applying liquid sealant to one of a marginal portion of the solid polymer electrolyte membrane , the marginal portion being not covered by the pair of electrodes when assembled , and a surface of each of the pair of separators , the surface corresponding to the marginal portion of the solid polymer electrolyte membrane ; holding the solid polymer electrolyte membrane with the pair of separators to perform temporary assembling ; and solidifying the liquid sealant while maintaining a temporary assembling state .