In order to clarify the relation between the diamond surface chemical structures and their surface potentials, we measured the surface work function change varied with the chemisorbed structures of the chemical vapor deposited diamond surfaces. The chemical vapor deposition of homoepitaxial diamond thin films yielded an atomically flat diamond surfaces appropriate for studying a diamond surface chemistry. The surface chemisorbed structure varied with increasing of the oxidized temperature in the range from R.T. to 500^oC. According to the surface chemisorbed structure, the surface potential change was observed. The oxidation temperature below 300^oC, little chemisorbed hydrogen on the diamond surface was abstracted and replaced to chemisorbed oxygen. In the temperature range, a slight decrease of surface potential was observed. The oxidized temperature in the range between 300∼420^oC, a hydrogen terminated diamond surface turned into an oxygen terminated one such as an ether and a ketone structure with increasing of the temperature. A drastic decrease of surface potential was observed with the surface structure variation.