A-C: H (Hydrogenated amorphous carbon) diamond like carbon(DLC) film is the low stabilities of chemical and mechanical properties at high temperatures. Some researchers reported that Raman spectra shown significant conversion of DLC films to nano-crystalline graphite on heating in ambient air at temperatures above 300°C and conversion to nano-crystalline graphite was completed by 450~600°C In this study, DLC films(thickness : 1.5-m) were deposited on p-type (100) silicon films by using C6H6 and C6H14 plasma produced with a 13.6MHz RF source. To investigate the mechanical stability of DLC films below 250°C, we thermally aged the films for different aging temperatures (150°C, 200°C, 250°C) and times (0: virgin, 120, 240, 360 hours). By using indentation test and Raman spectra analyses, it has been found that the H3/E2 decreases with increasing I(D)/I(G) ratio. Also we confirmed that sample-2(precursor gas: C6H14) had better mechanical characteristic and thermal stability than the sample-1(precursor gas: C6H6).