pH-responsive chemically reduced graphene/poly(acrylic acid) (PAA) assembly is simply formulated through noncovalent interaction. Graphene/PAA assembly shows optical absorbance change depending on pH of the solution. Structural rearrangement of graphene/PAA assembly might contribute this optical modulation at different pH through either "hydrophobic interaction dominating" mode in strongly acidic medium or "charge repulsion dominating" mode in strongly basic medium.