I Isolation transformer is a special transformer is used to supply power engine furnace due to the characteristics of an isolation transformer is to have a protection system in the circuit, isolation is the separation between the primary and secondary side, and an isolation transformer is suitable for loads that have characteristics of high frequency is not stable. This research aims to design a 1500 kVA isolation transformer that can supply the needs of the machine furnace. The design starts from the determination of the iron core and windings. And the magnitude of the value of voltage, current, and resistance that exist in transformer based formula. The data used is secondary data obtained from PT ASATA UTAMA. The data is in the form of large iron core, coil material, intibesi material and insulation material. The data will be validated with data obtained from the results of the design. The results showed that the difference lies in the iron core material, coil material, and the number of windings. Such differences do not affect the value of the voltage, current, and power generated.