Several types of starches were oxidized by H2O2 in the presence of iron tetrasulfophthalocyanine catalyst (FePcS) in batch mode, and the kinetics of the H2O2 decomposition was followed when varying the catalyst concentration and solid to liquid ratio of the starch and aqueous phase. Mainly, waxy corn starch with high content of amylopectin and potato starch were used, but also high amylose starch was studied. The COOH content was determined for the final oxidized starch. It was found that, with 40 mg of catalyst and the starch present in a larger amount, the H 2O2 decomposition followed a first order kinetics with an initial decomposition rate in the range of 0.10 mol/L·h. Significantly less starch slowed down the decomposition rate to 0.05 mol/L·h; however, when no starch was present, the decomposition increased to a maximum of 0.14 mol/L. On the contrary, absence of catalyst resulted in a linear H 2O2 decomposition profile. The FePcS catalyst concentration had a large impact on the decomposition of H2O 2 regardless of the starch amount or the starch origin. When using very low starch amounts in relation to the catalyst amount, brown solid residues were observed on the reactor wall, indicating that iron was defragmented from the catalyst.