AbstractElectron cyclotron resonance-discharge cleaning (ECR-DC) was carried out in tokamak experiments to reduce the impurities on the surface of plasma chamber, yielding good results. However, quantitative analysis for residual gases by long time ECR-DC has not yet been reported. In the TRIAM-1M device, the surface of the plasma chamber was cleaned using long time ECR-DC without baking the chamber, and clean plasmas were produced. The effects of ECR-DC were analyzed by the measuring of 17 (OH), 18 (H2O), 28 (CO) and 44 (CO2) with quadrupole mass analyzer (QMA).