The present invention is to provide a novel phosphodiesterase and a gene thereof, specifically, Type 11 phosphodiesterase (PDE11) and a gene thereof, more specifically, a phosphodiesterase selected from (A) a protein having an amino acid sequenced shown by SEQ.ID.NO: 2, SEQ.ID.NO: 4, SEQ.ID.NO: 6 or SEQ.ID.NO: 39, and (B) a protein having an amino acid sequence shown by SEQ.ID.NO: 2, SEQ.ID.NO: 4, SEQ.ID.NO: 6 or SEQ.ID.NO: 39 in which one or several amino acids are deleted, substituted or added, and having an activity of hydrolyzing a cyclic nucleotide, and a gene thereof, and a method of characterizing, identifying and selecting a phosphodiesterase inhibitor by using the same.