Abstract: The invention provides a detection method of protein-protein interaction that detects the interaction of a protein X with a protein Y having a reporter function in a eucaryotic cell, which comprises modifying the protein X and/or the protein Y to be expressed with different localization patterns in the cell, co-expressing the protein X and the protein Y in the eucaryotic cell, and identifying the intracellular localization of the protein Y by its reporter function that serves the index thereof. The invention also provides a method for detecting the inhibitory or promotive action of a compound Z on the interaction of the proteins X and Y in a eucaryotic cell.