IDO is an enzyme that tumors use to create a state of immunosupression. 1-d-methyltryptophan (1-MT) is an IDO pathway inhibitor. After being successfully evaluated in preclinical studies, current clinical trials are actually analyzing its efficacy as monotherapy or in combination with multiple chemotherapeutic agents such as paclitaxel. 1-MT very poor solubility in water and many other solvents precludes its ease parenteral administration. It is currently administered by oral route because high daily doses were well-tolerated and effectively inhibited the IDO activity although only 25% of dose was recovered in plasma. The present work describes the preparation and characterization of 1-MT nanocrystals in order to enhance its solubility, dissolution rate, biodisponibility as well as facilitate its administration by parenteral route. A bottom-down approach of nanoprecipitation with an antisolvent was used for the fabrication of the nanocrystals and the choice of stabilizers was critical for reducing the size. Thermal analysis and x-ray diffraction indicated modifications in the drug crystalline state by the process. Through the reduction size and crystalline state modifications the dissolution characteristics of raw material were significantly increased. In a Lewis Lung cancer mice model, the nanocrystals strategy facilitated the sc administration and its antitumoral activity was similar to that of i.v. paclitaxel. The best efficacy was achieved when sc 1-MT nanocrystals were administered in combination with oral paclitaxel loaded in poly(anhydride) nanoparticles. Take together, 1-MT nanocrystals delivery performs a nanotechnological strategy suitable to modify the current route and schedule for its administration.