Tribological properties of ultra nanocrystalline diamond (UNCD) and diamond nanorod (DNR) films are studied in ambient and nitrogen test atmospheres. Friction coefficient of UNCD films is found to be low in nitrogen and high in ambient test atmospheres using steel (100Cr6) and alumina (Al2O3) counter bodies. However, DNR films exhibit a high friction coefficient in nitrogen and a low value in ambient atmospheric conditions. Interestingly, in low humid conditions, the friction coefficient of UNCD decreases whereas it increases for the DNR films. Remarkable change in high/low friction coefficients of the UNCD and DNR films depending on test atmospheres is found to relate with the modification of internal chemical structures of these films. The distinct effect of the test atmospheres on the internal structure and chemistry of these films dominantly influence the interacting forces during the sliding interfaces. Internal characteristics of these film phase fractions such as sp3/sp2, nanocrystalline graphitic content and formation of carbonitrile phase are found to be the basic factors that influence the friction behaviors. Understanding the environmental dependent tribological properties of these films will be useful in the implementation of reliable micro- and nanoelectromechanical systems (MEMS/NEMS) in different test atmospheric conditions.