We modified polycarbonate by introducing chain extender in the extrusion process. The modified polycarbonate showed high G' depending on the content of the chain extender, though a change of G" was not significant. The elongational viscosity indicated unusual deviation from values estimated from the linear viscoelasticity. That suggests formation of the long-chain branching of the modified polycarbonate. We also studied batch-foaming behaviors of the modified polycarbonate.