This study demonstrates a sacrificial layer approach by co casting, which is the simultaneous casting of two layers, to prepare a polysulfone support (denoted as PSf(co)) layer with open bottom surface morphology for fabricating thin-film composite forward osmosis (FO) membranes. In the co casting process, polyetherimide (PEI), used as the sacrificial layer, was co cast beneath the PSI layer. After the PEI layer was peeled off, PSf(co) was yielded with an open bottom structure. Results showed that under the same operating condition, the FO membrane prepared by co casting (denoted as PSf(co)-TFC) demonstrated a 10% higher water flux using 0.5 M NaCl draw solution and 30% higher water flux using 4 M NaCl draw solution in the AL-FS mode in comparison to membranes prepared in a single layer casting technique (denoted as PSf(s)-TFC). The PSf(co)-TFC exhibits a lower average structural parameter (5, 167 mu m) than that of the PSf(s)-TFC (241 mu m), while the water and salt permeability coefficients of both membranes are similar. Results reported here demonstrate that the co-casting technique can be used to fabricate FO membranes with significantly improved performance compared to the conventional approach. (C) 2015 Elsevier B.V. All rights reserved.