The potential energy surfaces of four reactions including (a) HOCl + H, (b) HOCl + O, (c) HOCl + HO, (d) HOCl + HO2, have been studied by the CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVDZ, CCSD(T)/aug-cc-pVTZ//CCSD/cc-pVDZ, and CCSD(T)/6-311+G(3df,2p)//BH&HLYP/6-311+G(3df,2p) levels of theory. For both HOCl + H and HOCl + O, the direct Cl-abstraction channels take place via the lowest energy barriers; for both HOCl + HO and HOCl + HO2, the lowest energy barrier channels are the indirect H-abstraction reactions by HOx (x = 1, 2) via long-lived reaction intermediates. The rate constants for the low barrier channels have been calculated in the temperature range 200-3000 K by statistical theory. The predicted rate constants for HOCl + H and HOCl + HO are in good agreement with experimental results whereas that for HOCl + O was found to be in disagreement with the majority of available experimental data, suggesting a need for further improvement in theory and/or experiment.