Seawater desalination through the air gap membrane distillation (AGMD) process shows merit for its ambient operational conditions and low energy consumption. In this paper nine types of commercially available membranes were characterized to understand the membranes more comprehensively. The density, porosity, mean pore radius, liquid entry pressure (LEP), and contact angle (CA) of the membranes were determined. AGMD experiments were performed for the membranes to investigate the membrane difference on permeation flux and salt rejection. The effects of operating parameters such as temperature, flow rate, and NaCl concentration were studied. The 0.22 μm pore size PTFE membrane showed excellent performance for its higher permeability and higher hydrophobicity than other membranes. The mass transfer coefficients for three types of PTFE membranes were calculated from the results of the experiments.