The stress and strain in c-BN films deposited onto silicon substrate by hot filament assisted rf plasma chemical vapor deposition is determined by XRD analysis using the sin 2 ψ method and assuming an effective stress model. The compressive stress in c-BN is much greater than that in h-BN for the same film, when both c-BN and h-BN in the same film have similar amount of elastic strain. To investigate the validity of the effective stress model, the stress in the films was measured with a surface profilometer also. Residual stresses in the films were compressive and varied from 2.87 GPa to 12.1 GPa with increase in substrate temperature (700–1200°C). The dependence of the compressive film stress on c-BN content is also given in the present work. The increase of compressive film stress with increasing c-BN content is due to the elastic modulus of c-BN being greater than that of h-BN.