A series of tungsten oxide nanoparticles (NPs) has been synthesized via a green and straightforward approach exploiting bare tungsten powder as a precursor. The synthesized NPs were further organo-functionalized by cetyltrimethylammonium bromide (CTAB) in order to adjust their surface state and enhance their compatibility with biphasic oxidation of vegetable oils with H2O2. Simply, different structures of tungsten oxide were observed, which were characterized by XRD, FTIR, TGA, TEM, N-2 adsorption/desorption isotherms, and zeta potential analysis. All the synthesized nanocatalysts could fully convert oleic acid, and the highest yield of production of the desired diacid (azelaic acid), similar to 80%, was achieved by optimization of the CTA(+) amount on the nanocatalyst's surface, which show excellent activity compared to the reported heterogeneous works. Thanks to the organo-functionalization, this water-tolerant catalyst exhibited no significant leaching, as well as convenient recovery and steady reuse without a noticeble decrease in activity, at least up to four cycles.