To implement Condition Based Maintenance (CBM) on power transformer where its accurate condition became necessary and crucial, PLN P3B JB develop condition assessment method. This method starts with FMEA/FMECA generation to define critical failure modes and weighting factor which will be used to give optimal portion of inspections value and typical failure modes in defining condition of transformer.Next step is defining inspection method that accurate to assess those failure modes, whether it is visual inspection, in service measurement or shutdown measurement. Some calculation also used to combine all inspection values in order to generate result value that represents actual condition of transformer.