Oxidation resistance of diamond is an important characteristic to be considered in high-temperature microelectronics and other applications. We have tested the stability of CVD diamond by exposing it to Ground State Atomic Oxygen (GSAO, O) at a temperature of 74 degrees C. Polycrystalline diamond is quite stable at this temperature using O. We have also tested the stability of diamond using Excited State Atomic Oxygen (ESAO, O *). Initially, CVD diamond was exposed to O * for 15 min at 63 degrees C, and diamond etching was observed. We have also carried out the experiments at different time intervals such as 30 and 45 min. The etching rate of the polycrystalline diamond using O * is approximate to 0.2-0.25 mu m/min at 63 degrees C. We have successfully patterned the diamond (polycrystalline and single crystal) using a Ni mask by exposing the sample to O * for a longer time. O * etched the diamond uniformly in all the directions of the diamond crystal as opposed to the molecular oxygen. Stability of the single crystal diamond has been tested using O * by using Ni mask material. We were able to etch the single crystal diamond (type IIa, 100 orientation) quite uniformly. The etching rate of single crystal diamond using O * was observed to be 0.3 mu m/min.