The effect of salt, acid and base as additives on the decomposition of 2-chlorophenol (2CP) in supercritical water was investigated. Four additives were selected, NaCl as a salt, HCl and H2SO4 as acids, and KOH as a base. The addition of salts and acids had a little effect on the decomposition of 2CP in supercritical water (SCW), but that of bases showed a significant effect to enhance the decomposition rate.