In this paper, the dielectric properties of the mineral oil-based nanofluids was studied. The aim of this research is to improve electrical property of the mineral oil by applying nanotechnology knowledge. Three types of nanoparticle i.e. Titanium dioxide (TiO 2 ), Barium titanate (BaTiO 3 ) and Zinc oxide (ZnO) with the mean diameter less than 100 nm were used in the experiment. The nanofluid samples, the mineral oil mixed with nanoparticle, were prepared in three processes. Firstly, the mineral oil was mixed with 0.01% of nanoparticle volume fraction of nanoparticle. Besides, the mineral oil was also mixed with 0.03% of nanoparticle volume fraction. Then it was dispersed by using a magnetic stirrer. Finally, the ultrasonic dispersant technique was applied for the prepared nanofluids to ensure the homogeneity of such liquid. To measure the AC breakdown voltages, an oil breakdown tester (FOSTER OTS 60AF) was used. The gap distance between electrodes was set to be 2.5 mm. The testing was carried out 6 times for each liquid test sample according to IEC 60156. The test results showed that the AC breakdown property of the modified liquid was strongly influenced by the type of the nanoparticles added. With the addition of nanoparticles, the AC breakdown voltage increased slightly above that of the mineral oil (37 kV). In case of 0.01% nanoparticle volume fraction, the AC breakdown voltage of the mineral oil with TiO 2 , the mineral oil with BaTiO 3 and the mineral oil with ZnO was 42 kV, 45 kV and 46 kV respectively. For 0.03% nanoparticle volume fraction, the AC breakdown voltage of the mineral oil with TiO 2 , the mineral oil with BaTiO 3 and the mineral oil with ZnO was 45 kV, 48 kV and 60 kV respectively. From these results, it is indicated that nanoparticles is a good candidate to develop mineral oil-based nanofluids for dielectric applications.