Today, the use of electricity sources is increasing as cities are growing. With the increasing use of mineral oils for transformers cooling in the distribution network, due to the problems encountered using these oils, an alternative fluid should be used inside the transformers instead of mineral oils. Therefore, mineral oils should be replaced with fluids that are more compatible with nature due to the environmental hazards and high costs. Hence, vegetable oils can be used as suitable alternatives for the mineral oils in transformers due to their low risk and the renewability. On the other hand, compared to the mineral oils that have a fire point of about 151 Celsius degrees, vegetable oils have fire points higher than 311 Celsius degrees. As a result, from this viewpoint, they are considered as harmless fluids. Vegetable oils are simply degraded in the nature, and due to their different chemical structures compared to the mineral oils, they can increase the life of the equipment. Besides, the most important point is that they improve the transformer cooling performance, in terms of thermal analysis. Thus, in this paper, the distribution transformer electromagnetic-thermal analysis and conjugate heat transfer, in presence of different types of vegetable oils, and different types of cores such as grain-oriented silicon steel, amorphous and vitroperm alloy are investigated. Afterwards, the obtained results, especially hot spot temperature, are compared with distribution transformer containing mineral oil. ANSYS software has also been used for simulations.