In this paper, we used two simplified methods to understand the influence of surfactant molecular structure on the properties of surfactant DNA complexes. First. we selected Langmuir balance technique, a two-dimensional (2D) method, which allows complex formation under equilibrium-like conditions, avoiding some of the inherent problems involved in Solution. Secondly, two series of simple quaternary ammonium surfactants were used. The cationic surfactant-DNA complex monolayers were formed at the air-water interface through the electrostatic interaction between the ammonium groups of the surfactant and the phosphate groups of DNA at the air-water interface. Combining the results of pi-A isotherms, pi-t isotherms, and atomic force microscopy (AFM) measurements, it was found that the surfactant molecular structures affect the surface properties and morphologies of 2D surfactant-DNA complexes. We expect that the study of the properties of 2D surfactant-DNA complexes will help us to understand the physicochemical properties of surfactant-DNA complexes, which are important for gene delivery. (c) 2005 Elsevier Inc. All rights reserved.