This paper presents the results of an evaluation of the bridge health index for 830 bridges managed by the Gifu Prefectural authorities. The proposed bridge health index is statistically calculated using data from periodic inspections conducted by the authorities between 2001 and 2006. The database contains the results of five-step discrete data on many items set for decks, girders, expansions, shoes and accessories. The five-step grading is based on visual observation of the degree of deterioration for various members and components. However, due to the excessive amount of inspection items and components in bridges, the summarized grade obtained in this inspection is insufficient for making an effective repair and maintenance plan. Accordingly, indices that enable an overall evaluation of each bridge (or main components such as RC deck) is required. This study aims to express health indices for the RC decks of steel bridges using an overall indices based on principal component analysis, which can clarify identify the health condition of the bridges with deterioration mechanism.As a result, the principal componentwas confirmed, enabling identification of the main deterioration mechanism afflicting RC decks, whereas the second component suggests the mechanism of the deterioration. This methodology is considered to obtain useful information for bridge management, because the optimal timing for repairs and countermeasures differs depending on the deterioration mechanism.