An electrochemical reaction unit including a unit cell including an electrolyte layer, and a cathode and an anode that face each other in a first direction with the electrolyte layer intervening therebetween; and a felt member containing a ceramic material or a metal and a silica component. The felt member has an Si content of 0.9 mass % to 13.2 mass %. Also disclosed is an electrochemical reaction cell stack including a plurality of electrochemical reaction units, at least one of the units being the above-described electrochemical reaction unit.