In this study, nanofiltration performance of an ultrathin graphene oxide (GO) membrane was significantly improved by optimizing surface morphology of polycarbonate (PC) support via ion beam treatment. Ion beam can precisely control the dimensions of the wrinkled structure by adjusting exposure time. The wrinkle formation can be attributed to increased degree of polymer cross-linking and heat generation by penetrating Ar+ ions that result in a stiff skin layer. Upon filtration testing, water flux of the GO membrane with 20 nm thickness was enhanced by 6.4 times with wrinkled PC support. The root mean square (RMS) of the height was 0.83 nm for flat PC and 11.5 nm for wrinkled PC. A high rejection rate (greater than 90%) was also observed with dye molecules of sub-nanometer size. The influence of support morphology on the water flux was found to be especially significant when the thickness of the GO membrane was below 10 nm, which enhances the water flux from 4.21 L m(-2) h(-1) bar(-1) at an RMS of 0.827 nm-26.9 L m(-2) h (1 )bar(-1) at an RMS of 11.5 nm. These results indicate that the support morphology is a critical parameter that determines the performance of ultrathin graphene-based membranes. (C) 2019 Elsevier Ltd. All rights reserved.