The isomerization processes of 3-hydroxy-2(1H)-pyridinethione with water or water cluster in the aqueous solution were explored at B3LYP-D3/6-311++G(3df,3pd) level of theory. The results suggest that the formation of P2 dominates over that of P1 in the isolated reaction, whereas the barrier difference of transition states between them will decrease gradually with increasing of water number from one to three and the production of P1 will be competitive to that of P2 with water dimer or water trimer. Furthermore, the location of water or water cluster between N and S is more suitable for the formation of active component P1. (C) 2016 Elsevier B.V. All rights reserved.