TokyoGreen®-βGal is cell permeable fluorescent substrate (9-(4′-methoxy-2′-methylphenyl)- 6-(β-D-galactopylanosyloxy) -xanthen-3-one) for detecting β-galactosidase. Cell lysis or fixation is not required since TokyoGreen-βGal is easily incorporated into cells. TokyoGreen-βGal is applicable to the experiments of gene expression test, gene targeting and cell cloning utilizing lacZ gene marker.