The present work is part of a series of papers (1-3) dealing with the breakdown of pesticides into different chemical species upon heating in the presence of oxygen. Heating up of pesticides in the presence of oxygen occurs when cooking poisoned vegetables and when toasting or smoking tobacco, resulting in a possible harm to human health (4). The paper addresses thermal decomposition under oxidative conditions of three largely used Aldoxime carbamate insecticides: Aldicarb (2-methyl-2-(methylthio)propionaldehyde O-methylcarbamoyloxime), Aldicarb sulfone (2-mesyl-2-methylpropionaldehyde O-methylcarbamoyloxime) and Aldicarb sulfoxide (2-mesyl-2-methylpropionaldehyde O-methylcarbamoyloxime).Different decomposition ways have been suggested for aldoximes, and the aim of this work is to gather more information on thermal decomposition pathway of these compounds in an oxygen containing atmosphere. The experimental work consists of non isothermal thermogravimetric analysis with 5% oxygen in helium, using a TG-MS system equipped with a Skimmer device that ensures the simultaneity of the thermogravimetric analysis and of the analysis of evolved gas. The TG-DTG curves have been collected for each of the compounds and the MS spectral data has been compared with NIST spectrum data base. The experimental results give indication that the three examined pesticides undergo thermal degradation starting at about 150 °C. The pattern of thermal degradation as regards the fragmentation of the left side of the molecule is very similar for the three compounds. The fragmentation of the right hand side of the molecule produces instead somewhat different sulphur containing species. The role of oxygen in the reaction environment upon heating seems to be of minor importance.