This paper presents a risk assessment tool for power transformers in central region substations of Provincial Electricity Authority (PEA) by using health index, which is computing from history and condition weighted scores. The maintenance data from 237 power transformers in central region are used to analyze the risk factors' ranking and scores. The weights of the risk factors are assigned by experienced maintenance crews. The risk assessment factors and scores are categorized with equal weight into two parts: the history of the transformer; and the current condition of the transformer. The weighted scores from both parts are calculated to obtain the health index (HI) for the power transformer. The HI is then plotted on a square matrix called the "health-index matrix", which interprets the risk condition for that transformer. The risk assessment method proposed in this paper is applied to three power transformers in different load areas in central region of PEA. The results show that the method successfully detects the risk condition of those transformers. Therefore the proposed method can create an efficient preventive maintenance plans for power transformers in central region of Provincial Electricity Authority.