A method of producing an indwelling needle assembly formed by assembling an inner needle having a point only at its tip, an inner needle hub fixed to the base end of the inner needle, a hollow outer needle through which the inner needle is insertable, an outer needle hub fixed to the base end of the outer needle, and an elastic seal member on the outer needle hub effecting sealing when the inner needle is withdrawn. The method involves: inserting the inner needle into the seal member to set the inner needle to an inserted state; applying, in the inserted state, lubricant to the outer peripheral surface of at least that portion of the inner needle which protrudes from the seal member; and axially reciprocating at least one time the inner needle relative to the seal member to cause the lubricant to penetrate the inside of the seal member.