The paper focuses on studying the rheological properties of different vegetable oils mixed with TiO2 nanoparticles. The rheological tests of vegetable oils are conducted on cone and plate geometry of Anton Paars rheometer (MCR-102). TiO2 nanoparticles are added in 0.5 wt%, 1 wt% and 1.5 wt% concentration. The density of nanofluids is measured from 20–80 °C, and the viscosity of nanofluids is measured at temperatures of 40 °C, 70 °C and 100 °C. All the nanofluids depict Newtonian behaviour at different temperatures and are quantified by power law. The introduction of nanoparticles in the oils leads to the increase in viscosity with 1.5 wt% TiO2 concentration displaying maximum increase in viscosity in all the bio-oils. The variation of viscosity with temperature, shear rate and particle volume fraction is observed, and the measured values of viscosity are correlated with the existing theoretical viscosity models.