We succeeded in preparing a fibrous nanotube of green fluorescent protein by conjugation with poly(2-vinylpyridine) and use of a microfluidic synthesis technique. By inducing a sudden pH change in the acidic solution (pH 4.5) by injection into a neutral buffer using a microsyringe, the fibrous nanotube could be selectively formed. Its diameter and length were about 200 nm and 1-10 mu m, respectively.