The objective of this study is to reduce heavy oil viscosity through the catalytic decomposition of heavy fractions by ultrasound cavitation using metal oxide nanoparticles and water as a hydrogen donor, leading to the reduction of asphaltene content through its conversion into lighter components. NiO nanoparticles were synthesized over a 7 nm silica support using the incipient wetness technique. Emulsified heavy oil (HO) with 40%v/v of water and 13°API was used to evaluate the ultrasound cavitation process over different exposure times and nanoparticle dosages. The viscosity of the emulsified HO before and after ultrasound cavitation was measured with and without nanoparticles. Significant viscosity reduction was obtained, showing best results at 90 minutes of ultrasound exposure time with a nanoparticle dosage of 2000 mg/L, leading to a viscosity reduction at 10 s-1 and 25°C, and an asphaltene content reduction of 44 and 16%, respectively.