Diamond-like carbon films (DLC) 10–40 nm thick were deposited on quartz substrates on an interdigitated planar array of 20 μm Ni electrodes already prepared by lithographic techniques. The influence of the adsorbed molecules onte electrical properties of the thin DLC films was investigated. Current and capacitance-voltage characteristics were examined. Charge-based deep level transient spectroscopy (Q-DLTS) was used for study of adsorption and desorption processes. The strong sensitivity of Q-DLTS spectra to the presence of the vapor water and isopropyl alcohol was found. For example, the Q-DLTS signal for some deposited DLC film was changed more then in order in presence of the water vapor. Such strong surface phenomena of the thin DLC films may be exploited in novel gas sensor devices.