A low-frequency after-glow capacitively coupled plasma discharge technology is employed to prepare sulfonated plasma polymerized membranes. In comparison with conventional Nafion (R) 117, these plasma polymerized membranes usually exhibit dense and uniform structures with a thickness adjustable by the deposition time, and show great promising in the applications of DMFCs. Due to the complexity of plasma polymerization, however, the qualities and properties of the fabricated membranes are strongly dependent upon the synthesis conditions. Therefore, to achieve the membranes with desirable properties for direct methanol fuel cell applications, such as high sulfonation contents, high chemical, mechanical, and dimensional stabilities, high proton conductivity and lower methanol permeability, the conditions used for the membrane synthesis must be optimized. It shows that these membranes synthesized under preferable conditions possess highly cross-linked structures, higher sulfonation contents and chemical and mechanical stabilities, and therefore exhibit superior properties, such as higher proton conductivity and lower methanol permeability, in their applications in direct methanol fuel cells. (C) 2011 Elsevier B.V. All rights reserved.