The oxidation of dimethylether (DME) has been studied experimentally at low-temperature (550-800 K) in a jet-stirred reactor operating at I atm. The mutual sensitization of the oxidation of dimethylether and NO was also studied. It was shown that above 600 K, NO enhances the oxidation of DME in the cool flame regime and yields methylformate (not formed without NO) whereas NO is oxidized to NO2. Below 600 K, the oxidation of DME was inhibited by NO. A detailed chemical kinetic model was developed to simulate the present experiments and the ignition of DME/air mixtures in shock tube at 13 and 40 atm. A good agreement between the experimental results and the modeling was generally obtained. According to the proposed kinetic mechanism, in the present conditions, the mutual sensitization of the oxidation of DME and NO proceeds through the following sequence: DME + OH --> CH3OCH2(R); R + O-2--> RO2; RO2 + NO --> RO + NO2; RO --> methylformate + H; RO + O-2 --> methylformate + HO2; HO2 + NO --> OH + NO2. The inhibition of DME oxidation below 600 K is due to RO2 + NO --> RO + NO2 that reduces the production of OH by competition with the isomerization RO2 --> QO(2)H responsible for chain-branching: QO(2)H + O-2 --> O(2)QO(2)H HO(2)Q'O + OH; QO(2)H --> 2CH(2)O + OH; HO(2)Q'O --> OQ'O + OH.