An object of the present invention is to provide a production method for a synovium-derived mesenchymal stem cell, which makes it possible to obtain a sufficient amount of synovium-derived mesenchymal stem cells from the synovial tissue, a production method for a cell preparation for joint medical treatment using the production method for a synovium-derived mesenchymal stem cell, synovium-derived mesenchymal stem cell, and a cell preparation for a joint medical treatment. According to the present invention, there is provided a production method for a synovium-derived mesenchymal stem cell, which includes treating a synovial tissue with an enzyme for 2 hours or more; and washing a mixture after the enzyme treatment until a residual enzyme concentration in a supernatant is 0.5 ng/mL or less, to obtain a synovium-derived mesenchymal stem cell.