In this study, we propose a convenient method for the synthesis of double-network gels by the one-shot radical polymerization for their application to rapid optical tissue clearing. Double-network gels were produced during the radical polymerization of acrylamide (AAm) and sodium styrenesulfonate (SS) in the presence of N,N′-methylenebisacrylamide and sodium divinylbenzenesulfonate as the cross-linkers by simultaneous addition, that is, one-shot polymerization accompanying the delay of polymerization for a second network monomer. We analyzed the polymerization process based on the consumption rates of each monomer during the reactions in the absence of the cross-linkers in order to estimate the repeating unit structure of the resulting polymers. We then fabricated the AAm/SS gels by the polymerization of AAm and SS in the presence of the cross-linkers. We analyzed the swelling, viscoelastic, and mechanical properties of the produced gels to investigate their network structure. Finally, we demonstrated the validity of the double-network gels for the application to rapid optical tissue clearing.