Effect of adding nanofillers on transformer oil breakdown voltage and its thermal performance finds a great interest from researchers and scientists. The impact of oil circulation considering oil forced cooling method on nanoparticles stability in transformer oil is investigated. The stability is considered from breakdown voltage and thermal performance points of view. Titanium dioxide (TiO2) nanoparticles are chosen due to the safety of TiO2 nanomaterial as well as its good performance. First, the optimal concentration of nanosized TiO2 at which maximum breakdown voltage of nanofilled transformer oil is determined and chosen to study the effect of oil circulation on breakdown voltage as well as thermal performance of nanofilled oil. Two reduced experimental models are designed. The first model consists of a galvanized steel tank containing TiO2‐nanofilled transformer oil, at the pre‐determined optimal concentration. This tank is designed to simulate the natural oil cooled transformer. However, the second model that uses a similar tank is designed to simulate a forced cooled transformer. This model consists of a tank containing TiO2‐nanofilled transformer oil, at the pre‐determined optimal concentration, and an oil pump. Breakdown voltage and thermal performance considering the two adapted models are measured in a time period of 60 days.