ct— In order to maintain the life time of oil transformers and to improve their performance, the transformer oil must play its role as insulating and cooling medium efficiently. Nanotechnology is an effective science used for improving the dielectric and thermal properties of the transformer oil. In this paper, barium titanate (BT) nanoparticles were dispersed into the pure transformer oil by 0.01 g/L and 0.02 g/L concentration. Breakdown voltage and heat transfer coefficient were measured to excogitate the transformer oil dielectric and thermal properties, respectively. From the obtained results, for 0.01 g/L sample, it is noticed that BT nanoparticles enhances the heat transfer coefficient of the transformer oil by about 28.3% compared with the pure transformer oil but, the dielectric breakdown strength were slightly increase by about 2% only. The increasing of the BT nanoparticles concentration to 0.02 g/L achieves unsatisfied results due to the agglomeration and the sedimentation of BT nanoparticles into the transformer oil.