The decomposition characteristics of CF4 with Argon or oxygen in 2.45GHz microwave has been investigated by using a Langmuir probe with variation of the microwave power and chamber pressure. For CF4/Ar and CF4/O2/Ar discharges, the ion density and the electron density decrease with increasing microwave power. The electron temperature was decreased by reducing the mean free path of electrons with increasing microwave power. Also with increasing pressure, the electron temperature increase, and ion and electron density decrease by increase of inelastic collision frequency and of collision with the walls in the chamber. The electron temperature is 13.6 ~ 5.9 [eV], the electron density is 4.4×1010 ~ 2.2×1010 [cm-3] and ion density is 5.2×1011 ~ 4×1010 [cm-3]. According as add oxygen, ion and electron density increased relatively comparing to CF4/Ar discharge. The electron temperature is 8.5 ~ 6.2 [eV], the electron and ion density is 5.1×1010 ~ 2.1×1010 [cm-3] and 3.7×1011 ~ 7.3×1010 [cm-3], respectively.