To obtain a green fluorescent protein(GFP) having excellent fluorescent specific characteristics even under a wide range of pH condition.

A gene encoding the protein of the following (a) or (b) is obtained: (a) a protein comprising a specific amino acid sequence derived from the genus Aequorea; or (b) a protein which comprises an amino acid sequence obtained by deleting, substituting or adding at least one of amino acids to the above amino acid sequence and has the function showing stable fluorescent specific characteristics in an acidic domain. Further, two kinds of genes encoding a specific protein derived from the genus Aeqorea different from the above protein and the cyan-green fluorescent protein encoded by a series of these genes are obtained. Furthermore, a method for producing the fluorescent protein by the transformant containing the above gene as a recombinant vector is provided.