Supercritical water oxidation was used to break down municipal excess sludge. The reaction was carried out in a batch reactor with hydrogen peroxide as an oxidant in the temperature range of 473 K - 873 K. The reaction products were analyzed in terms of total organic carbon (TOC), organic acids and ammonium ion. TOC decreases with temperature and oxidant amount. Acetic acid and ammonia are detected as major refractory intermediates in the product. When more than the stoichiometric demand of oxidant is used, organic carbon in liquid phase is almost completely destroyed. Complete destruction of ammonia produced during the reaction requires higher temperatures than that of acetic acid.