The sulfonic acid (SO3H) group was attached to polyethylene by radiation-induced graft polymerization of sodium p-styrenesulfonate and compared with the SO3H group introduced into the polystyrene chain cross-linked with divinylbenzene. The catalytic activities of the SO3H group were measured in a batch mode for the hydrolysis of methyl acetate and sucrose. The temperature dependence of the reaction rate constants for the hydrolysis was determined. For the hydrolysis of methyl acetate, the SO3H group anchored to the grafted polymer chain had the same activity as the SO3H group introduced into the cross-linked polymer chain. On the other hand, the graft-type acid catalyst had about 10 times the hydrolytic activity for sucrose as the cross-linked acid catalyst.