Polysulfone (PSf) flat-sheet membranes with bi-continuous porous surfaces for direct-contact membrane distillation (DCMD) were successfully fabricated using a vapor-induced phase separation (VIPS) method. The present investigation revealed how the surface and cross-sectional morphology of PSf membranes and the desalination performance in DCMD were affected by exposure time, PSf content and relative humidity of air. In the VIPS process, an increase in exposure time led to a replacement of the bi-continuous top surface with a dense skin and to a large decrease in the permeate flux in DCMD. The best PSf membrane fabricated in this study had a mean pore radius of 0.32 mu m, water contact angle of 106.4 degrees, the liquid entry pressure of water of 300 kPa, and total porosity of 82.1%. During the DCMD process with a 35 g/L sodium chloride solution, the best membrane produced a permeate flux of 30.0 kg m(-2) h(-1) and a very low conductivity of distilled water at hot-feed and cold-distillate side temperatures of 73 degrees C and 25 degrees C, respectively. The thickness of the hydrophobic layer of the membranes was first measured using the weight method, and its value was used in a simulation of the DCMD process. (C) 2013 Elsevier B.V. All rights reserved.