In this paper, the influences of composition of copolymers and acidity of electrolyte in an electrochemical reactor on morphological structure of copper-in-polymer gradient composite film were investigated. For binary copolymers, poly(acrylonitrile-co-methyl acrylate) [P(AN-co-MA)] and poly(acrylonitrile-co-sodium allyl sulfonate) [P(AN-co-SAS)], the charged group -SO3- in P(AN-co-SAS) improves the swelling of the copolymer phase and copper reduction to form gradient morphology; the carboxylic ester group in P(AN-co-MA) is not effective because of its poor hydrophilicity, but it is a cooperating component with P(AN-co-SAS) to avoid excess of counterion (i.e., Na+) in SCF, which might severely interrupt Cu2+ coexistence. The swelling of the polymer phase is helpful to decrease the energy of the transfer ions in SCF and to enhance copper deposition and gradient formation. The increase of surface energy because of cluster growth raises the surface energy level of deposited Cu-0 clusters. The conteraction between these two energy factors allows the size of clusters to be 50-100 nm. The appropriate H+ concentration improves active Cu2+ reduction and thus deposited gradient copper phase in the copolymer matrix. (C) 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 373-380, 2004.