Conversion of vegetable oils to biodiesel typically involves the use of highly corrosive acids or bases as catalysts. Solid catalysts can be used to avoid the use of corrosive mineral acids/bases and they have the possibility of reuse. Development of a highly active solid acid based on graphene oxide that can be recovered using magnetic seperation and reactivated by simple washing is reported here. High catalytic activity of the iron oxide supported on sulphonated graphene oxide (GO-Fe2O3-SO3H) was established for the esterification of oleic acid as well as single step biodiesel production from waste cooking oil (WCO) using ethanol. Catalytic activity of GO-Fe2O3-SO3H was higher than GO, GO-SO3H as well as GO-Fe2O3. Thorough characterization of the prepared catalysts was done using a number of spectroscopic, thermal and microscopic techniques. Complete conversion of oleic acid to its ethyl ester could be done in 4 h, at 100 degrees C using 5 (% by wt.) of the catalyst. Moreover, single step conversion of WCO to biodiesel could be achieved at 90 degrees C in 6 h using 5 wt % of the catalyst. The catalyst was reclaimed by magnetic separation and reused upto 7 cycles without any significant loss of activity. (C) 2018 Elsevier Ltd. All rights reserved.