Mechanical properties and atomic bond structure of Si incorporated diamond-like carbon (Si-DLC) films were investigated. The films were deposited by 13.56 MHz r.f.-plasma-assisted chemical vapour deposition (r.f.-PACVD), using mixtures of benzene and diluted silane (SiH/H-2 10:90) as the reaction gases. Si concentration in the film was varied from 0 to 17 atomic (at.)% by increasing the diluted silane fraction from 0 to 95%. It was observed that the mechanical properties of the film changed significantly when the Si concentration was less than 5 at.%. In this concentration range, hardness, residual stress and elastic constants increased with increasing Si concentration. For higher concentrations of Si, the mechanical properties showed saturated behaviour. The changes of the mechanical properties are discussed in terms of the content of three-dimensional inter-links of the atomic bond network.