Diamond like carbon (DLC) films were deposited (thickness 100-130 nm) by RF plasma CVD of ethylene on to mica and silicon substrates at room temperature. Optical properties of the films deposited at different negative self bias (V B ) voltages (0 to -805 V) were measured. The refractive index (n) and extinction coefficient (k) of DLC films on mica varied within 1.6-2.1 and 0.035-0.128, respectively while the band gap energy (E g ) decreased from 2.38 to 2.01 eV with increase in V B from 0 to -805 V. The internal stress (compressive in nature) of these films (on mica) along with that of films deposited by sputtering of vitreous carbon target (on glass) was obtained from the broadening of the optical absorption band fail. The stress on mica (0.2-1.0 GPa) was observed to be comparable to the stress on silicon substrates (0.18-2.1 GPa), measured by the flexure of beam technique. The hardness of DLC films on mica varied within 6.5-8 GPa while that on Si varied within 6-9.5 GPa. The hardness of sputtered films on glass substrate was 8.7 GPa.