Relation between the electrical and optical properties of p‐type NiO films prepared either by RF sputtering or by the molecular precursor method is studied in terms of changes in crystallinity, resistivity ρ and absorption coefficients α. Values of α are correlated with electronic structures near the valence band maximum, which are obtained from the X‐ray photoelectron spectroscopy measurements and the density functional theory calculations. The ρ and α values are found to be strongly influenced by the crystallinity as well as the Ni vacancies as acceptor‐type intrinsic point defects.