Abstract Of the treatment and conversion technologies used for municipal sludge, wet oxidation has become an important process owing to the characteristics of water as a reaction medium at elevated temperature and pressure. This study aimed to investigate the non-catalytic wet oxidation of municipal sludge and degradation of solids, organic matter and other compounds. A digested sludge consisting of primary and secondary sludges was subjected to 60min wet oxidation at temperatures ranging between 220 and 240°C and oxygen to biomass ratios of 1:1–2:1. Wet oxidation was effective at degrading the organic solids, with maximum degradation of 86% for total suspended solids and 96% for volatile suspended solids. The concentration of oxidisable organic matter was reduced by 98% of the untreated sludge. It was found that reaction temperature has the most significant impact on sludge oxidation.