The present invention provides a thermoelectric conversion device layer having excellent durability and a method of producing the same. Specifically, the present invention provides a thermoelectric conversion device layer including a thermoelectric conversion module including, on one face of a film substrate, a thermoelectric element layer in which a P-type thermoelectric element layer and an N-type thermoelectric element layer are alternately arranged to be adjacent to each other in the in-plane direction and disposed in series; and further a sealing layer on the face side of the thermoelectric element layer, wherein the sealing layer has a water vapor transmission rate at 40° C. and 90% RH, as prescribed in JIS K7129:2008, of 1,000 g·m−2·day−1 or less; and a method of producing the same.