Polyvinyamine (PVAm) Fixed-Site-Carrier (FSC) composite membrane has been reported to have a good potential to be applied for large scale for CO2 capture applications with respect to high permeance and high selectivity. In this study, the membrane was investigated with respect to pH of the casting solution as a step for optimization of the membrane. It was found out that the pH of the PVAm casting solution could be easily controlled with a simple agent. The degree of protonation of the functional groups depends on the pH of the casting solution and influenced the reaction of carriers with CO2 and the solubility of CO2 in the FSC membrane swollen by water vapor in the feed flue gas. So it was expected that the pH could affect greatly the membrane’s CO2 capture performance. Membranes from casting solutions of different pH have been prepared, characterized and tested in a permeation set-up for CO2 separation from humidified flue gas. Permeation tests have shown that the performance of the PVAm FSC membrane for CO2 capture could be enhanced remarkably by pH control. This is explained by the increased number of free amine groups available for facilitated transport of CO2 with increasing pH. At low pH, it is assumed that the decreased number of free amines and the increased viscosity of casting solution have resulted in the decreased membrane performance.