SO3H-bearing amorphous carbon prepared from polyvinyl chloride (PVC) is studied as a heterogeneous Brønsted acid catalyst. Sulfonation of partially carbonized PVC produces amorphous carbon consisting of small SO3H-bearing carbon sheets linked by sp3-based aliphatic hydrocarbons. This carbon material exhibits much higher catalytic performance in the hydrolysis of cellobiose than conventional heterogeneous Brønsted acid catalysts with SO3H groups, including SO3H-bearing amorphous carbon derived from cellulose. This can be attributed to a high density of SO3H groups and the fast diffusion of reactants and products enabled by a flexible carbon network.