Four edible oils, and five mixtures consisting of oil and water in different ratios were heated to investigate the effect of water on the emission characteristics of particles generated by heating cooking oil. The PM2.5 and 0.01–10 µm particles emitted during the oil-water heating were monitored with a DustTrak, a condensation particle counter and an Aerodynamic Particle Sizer. The results showed that the PM2.5 mass concentrations and particle number concentrations when heating corn and peanut oil-water emulsions were up to 6 and 50 times higher, respectively, than when heating soybean and canola oil-water emulsions. Emulsions with an oil-water ratio of 6:1 all generated total particle concentrations that exceeded those of mixtures with other ratios. The promoting factors (normalized by the corresponding oil volume to the total volume) for the concentrations of the ultrafine particles, PM1 and PM2.5 ranged from 1.20 to 3.32, 1.14 to 2.50 and 0.71 to 2.14, respectively. In addition, the ratio between the ultrafine particles (10–100 nm) and the total particles, and the particle number mode and median diameters changed with the oil-water ratio, but no clear trend was observed. Regression analysis revealed that the effect of water on particle emissions is not statistically significant.