Phenylgalactoside, yomwe imadziwikanso kuti p-nitrophenyl β-D-galactopyranoside (pNPG), ndi gawo lapansi lopangira lomwe limagwiritsidwa ntchito pafupipafupi pakuyesa kwa biochemical ndi ma cell biology.Amagwiritsidwa ntchito nthawi zambiri kuti azindikire ndikuyesa ntchito ya enzyme β-galactosidase.
Phenylgalactoside ikakhala ndi hydrolyzed ndi β-galactosidase, imatulutsa p-nitrophenol, yomwe ili ndi mtundu wachikasu.Kumasulidwa kwa p-nitrophenol kungayesedwe mochulukira pogwiritsa ntchito spectrophotometer, popeza kuyamwa kwa p-nitrophenol kumatha kuzindikirika pamtunda wa 405 nm.