The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + 3NH (X3Σ-) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + 3NH (X3Σ-) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k1(HCl + HNO) = 4.7 × 10-8(T-1.08) exp(-129/T), k2(Cl + NH2O) = 1.7 × 10-9(T-0.62) exp(-24/T), k3(HOC1 + NH) = 4.8 × 10-29(T5.11) exp(-1035/T), and ktotal = 5.0 × 10 -9(T-0.67) exp(-1.2/T), respectively, with units of cm3 molecule-1 s-1, in the temperature range of 200-2500 K.