An electron cyclotron resonance (ECR) system has been assembled and microwave plasma was studied in argon, oxygen, carbontetrafloride, and a mixture of oxygen and carbontetrafloride. A cylindrical Langmuir probe was used to measure the current and its variation with respect to input power (50-1000 W), flow rates, probe position in the reactor and pressure. Plasma parameters like ion density N-i, floating potential, electron temperature and plasma potential were estimated. Optimum operational parameters like input power, pressure and gas flow rate were also established.