A process for producing a mass transfer device is provided which enables
packing of a packing material uniformly in a flow channel, and transfers
a specified substance by flowing a fluid containing the specified
substance through a flow channel on a substrate. A mass transfer device
produced by the process is also provided. The process for producing a
mass transfer device comprises steps of preparing a substrate, forming a
flow channel on the surface of the substrate, applying a liquid drop
composed of a packing material and a liquid medium, and packing the
packing material in the flow channel by removing the liquid medium.