Kinetics and mechanisms for NH3 reactions with ClOx (x = 0-4) radicals have been investigated at the G2M level of theory in conjunction with statistical theory calculations. The geometric parameters of the species and stationary points involved in the reactions have been optimized at the B3LYP/6-311+G(3df,2p) level of theory. Their energetics have been further refined with the G2M method. The results show that the H-abstraction process is the most favorable channel in each reaction and the barriers predicted in decreasing order are OClO > ClO > Cl > ClO3 > C1O 4. All reactions were found to occur by hydrogen-bonding complexes; the rate constants for these complex metathetical processes have been calculated in the temperature range 200-2000 K by the microcanonical VTST and/or RRKM theory (for ClO4 + NH3) with Eckart tunneling and multiple reflection corrections. The predicted rate constants are in good agreement with the available experimental data.