The present invention provides a process for producing a flexible optical waveguide which comprises the steps of: immersing a substrate having an optical waveguide formed thereon in water to thereby reduce adhesion between the optical waveguide and the substrate and then peeling the optical waveguide from the substrate; temporarily bonding the peeled optical waveguide to a surface of a pressure-sensitive adhesive layer containing a foaming agent; cutting the temporarily bonded optical waveguide into a given length; allowing the foaming-agent-containing pressure-sensitive adhesive layer after the cutting step to foam by heating, thereby reducing adhesion between the foaming-agent-containing pressure-sensitive adhesive layer and the optical waveguide; and peeling the optical waveguide cut into the given length from the foamed adhesive layer.