AbstractStudies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH2OH + 2I2= N2O + 4I−+ H2O + 4H+. Since the reaction is first‐order in [I2] + [I3−], the specific rate law,k0, isk0= (k1+k2/[H+]) {[NH3OH+]0/(1 + Kp[H+])} {1/(1 + KI[I−])}, where [NH3OH+]0is total initial hydroxylamine concentration, andk1,k2, Kp, and KIare (6.5 ± 0.6) × 105M−1s−1, (5.0 ± 0.5) s−1, 1 × 106M−1, and 725 M−1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH2OH) and molecular iodine (I2) as reactive species, with intermediates NH2OI2−, HNO, N