Different reactant ions including; CH 5 + , NH 4 + , NO + and H 3 O + have been used in soft ionization. Among those, NO + , NH 4 + and H 3 O + do not react with air components but react very fast with major inorganic compounds. H 3 O + which ionizes compounds via proton transfer reaction is the major reactant ion in ion mobility spectrometry (IMS). In this work, a method has been introduced to produce NO + as the major reactant ion in IMS. Having two independent reactant ions (NO + and H 3 O + ) gives the possibility of detection of more compounds. In addition when two compounds have similar spectrum with H 3 O + , they may be distinguish by use of NO + reactant ion. Unlike the H 3 O + , humidity has minimum effect on NO + chemistry so that NO + is the best reactant ion in the presence of humidity. NO + is slightly produced in corona discharge when oxygen presents. Although the abundance of NO + produced in the corona discharge increased with temperature, voltage and the oxygen content, at the highest value, its peak has lower intensity than that of H 3 O + . So several other methods; such as the reaction between nitric acid and cupper, or sulfuric acid and sodium nitrite were tried produce NO. The best method was found to be the use of arc in air. In addition, a disk was used in the front of the needle to prevent entering sample to the corona region. Hence, the product ions were purely due to the reaction between NO + and sample. After successful production of NO + , ion mobility spectra of aromatics, narcotics, explosives and thiols were separately recorded with both NO + and H 3 O + reactant ions. Comparison of IMS spectra showed that the major peaks for a substance with two reactant ions are different. In the case of NO + ions were mainly in the form of M + or M.NO + while for the case of H 3 O + they are MH + . In some cases, like benzene, the use of NO + gave more sensitivity.