We report sustainable novel simple green synthetic strategy to synthesize NiO nanocrystals. This is first report on sustainable biosynthesis of NiO nanocrystals employing Nephelium lappaceum L., peel extract as a natural ligation agent. Green synthesis of NiO nanocrystals was carried out via nickel-ellagate complex formation using rambutan wastes. Successful formation of NiO nanocrystals was confirmed. Possible mechanism of NiO nanocrystals formation using rambutan extract was proposed. Prepared NiO nanocrystals were coated on cotton fabric and their antibacterial activity was analyzed. © 2014 Elsevier B.V.