This study was conducted to investigate the effect of inorganic salts on the mass-transfer coefficient of O-3 and decolorization of azo dye (Acid Red 14, AR14) solution through ozonation in a microporous tube-in-tube microchannel reactor (MTMCR). The overall volumetric mass-transfer coefficient (K(G)a) of O-3 in the MTMCR was deduced by material balance. The effects of different salts on the K(G)a of O-3 and decolorization efficiency of the AR14 solution were studied, and results show that both were significantly affected by the inorganic salts. Although the K(G)a of O-3 and the decolorization efficiency of AR14 increased with increasing salt concentration and pH, the effect of NaNO3 was much weaker than that of NaCl, Na2SO4, Na2CO3, and NaHCO3. The enhanced K(G)a of O-3 and decolorization could be due to the generation of species with high oxidizing ability in the presence of the salts.