The homogeneous precipitation method was used to synthesis ZnO, NiO nanoparticles and ZnO–NiO nanocomposites with and without surfactants, sodium dodecyl sulphate (SDS) and hexamethylenetetramine (HMT) to alter the composition of nanocomposites. The grown samples were annealed at 300 °C and 600 °C for 2 h to convert the hydroxides into their oxides. To investigate the effect of different composition on the crystal growth, particle size, morphology, structural and optical properties of nanocomposite, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy (UV), Raman spectroscopy and Scanning electron microscopy (SEM) were employed. X-ray quantitative phase analysis was used to estimate the volume fractions of ZnO and NiO phases in grown nanocomposites. The percentage of ZnO phase is more than NiO phase in all nanocomposites and strongly depends on composition. The structural parameters like lattice constants (a, c), bond-length (l), unit cell volume (v), density (ρ), d-spacing (d), strain (ε) and dislocation density (δ) of ZnO, NiO and ZnO–NiO nanocomposites were calculated. The Scherrer, Williamson-Hall and Size-Strain analysis were used to calculate the crystallite size and lattice strain. The optical parameters such as optical absorption coefficient (α), bandgap (Eg), skin depth (δ), optical density (Dopt), extinction coefficient (k), refractive index (n), optical conductivity (σopt) and dielectric constants (εr, εi) were studied from UV–vis spectra. The nanocomposites grown in this study provide an opportunity of band tuning for better functional performance for device fabrication compared to the basic metal oxides. FTIR characteristic peaks and Raman fundamental optical phonon modes confirmed the formation of ZnO, NiO and ZnO–NiO nanocomposites. SEM analysis revealed that ZnO–NiO nanocomposites have different surface morphology by adding different surfactants.