A β-galactosidase activatable fluorescent turn-on theranostic Gal-CGem exhibits gemcitabine release specifically in β-galactosidase overexpressing hepatic carcinoma cells. The cytotoxicity of Gal-CGem in cancer cells is achieved through the apoptotic cell death pathway. Overall, Gal-CGem is a new frontline prodrug in cancer therapy that has provided antineoplastic information through fluorescence imaging.