The formation of head smear from DLC films on magnetic disks was confirmed by a simulated heating experiment. DLC films of 100-nm thickness were prepared and heated on a hot plate in an environmental gas chamber. Smear on a silicon wafer placed 3 mm above the DLC surface was observed after heating of the DLC film. The smear amount was quantified using the carbon intensity of the smear measured by XPS. In air, the carbon concentration decreased with the heating temperature; however, the carbon concentration increased with temperature in nitrogen. The carbon concentration of the smear in the air environment was smaller than that of nitrogen. As the result of comparison of smears on DLCs with various hydrogen concentrations, more decomposed gas is generated from the DLC film as the amount of hydrogen contained in the DLC increases, and this value increases at lower temperatures. This result suggests that DLC films with low hydrogen concentrations generate a smaller amount of decomposition gas than those with high hydrogen concentrations during heating. In addition, Raman spectra suggest that the DLC degraded by heating and the hydrocarbon gas-like materials were generated from the DLC film because the DLC films include carbon and hydrogen. Because fragments of 250–500 atomic mass units were observed in the TOF-SIMS spectra of smears, the smear is estimated to consist of a hydrocarbon of relatively high molecular weight.