In this work, Fe2O3, ZnO, and MgO nanoparticles were synthesized via a chemical precipitation method to investigate their effects on wax formation, morphological characteristics, and rheological behavior in a crude oil sample. For this purpose, differential scanning calorimetry, cross-polarized microscopy, and viscometry have been utilized as the main experimental techniques. It was observed that ZnO and MgO nanoparticles had the most positive effect on the wax appearance temperature (WAT) of the crude oil by reducing the WAT from 25 °C to 19.2 and 17 °C at 500 ppm, respectively. However, Fe2O3 nanoparticles did not have an acceptable efficiency in postponement of WAT. Addition of the nanoparticles into the crude oil caused deformation of wax crystals to more spherical and regular structures. In addition, presence of the synthesized nanoparticles prevented formation of the strong three-dimensional lattice of wax structures at high temperatures. XRD analysis of the wax deposits extracted from the crude oil showed that no chemical bonding occurred between the nanoparticles and wax molecules. However, superior size-dependent properties of the nanoparticles are responsible for controlling the growth of wax crystal nuclei and reduction of the WAT. Field-emission scanning electron microscopy images of the wax deposits showed a smooth and layered surface of the wax with some fine particles, which confirm physical interaction of the nanoparticles with wax. Findings of this work reveal the potential of ZnO and MgO nanoparticles as efficient and low-cost additives for production, storage, and transportation of the waxy crude oil.