Hexavalent chromium is an environmental concern due to its toxicity. So, to be treated, a contaminated solution can be concentrated or Cr(VI) can be removed. One of the possible technologies that can be used with this purpose is membrane separation. This work used a synthetic effluent with 570 mg L-¹ Cr(VI) for studying the fouling mechanism of nanofiltration process with a commercial membrane of polyethersulfone. Based on the permeate flux profile, the fouling mechanism was best described by the cake filtration model. Also, as the permeate chromium concentration did not vary during the process, Cr(VI) did not remain in the membrane and therefore the solution was not concentrated.