A novel high frequency coaxial transformer (HFCT) used for isolation in a DC/DC converter for solar PV power systems is presented. The winding structure is designed to counteract the proximity effects, and decreases the leakage inductance and the coupling capacitance between the primary and secondary windings. The experiment results demonstrate that this newly developed HFCT has achieved a very low winding loss and low leakage inductance, and a relative small coupling capacitance over a frequency range from 0.1MHz to 1MHz compared with a conventional high frequency transformer. The voltage ratio of the transformer is in good agreement with the turns ratio over the aforementioned frequency range. The simulation results confirm that the uniform distributions of magnetic flux and current density in the HFCT have been achieved.