To provide a method for treating the inner wall of a hollow fiber so that a gel to be filled into the hollow portion is physically or chemically fixed to the inner wall of the hollow fiber, and to provide a method for filling the gel into the hollow portion of the hollow fiber, which is suitable for use in micro-arrays for capillary electrophoresis and DNA analysis.

This method for introducing the hydrophilic functional groups into the inner wall portion of the hollow fiber comprises adhering the impermeable solution of a polymer having the hydrophilic groups to the inner wall portion of the hollow fiber. The method for filling the gel into the hollow portion of the hollow fiber is characterized by adhering the polymer to the inner wall portion and then filling the gel into the hollow portion.