In this study, the fatigue damage levels of practical RC road bridge decks was evaluated focusing on the decline of resonance frequency by forced vibration test. The bridge decks were replaced after being in service for 50 years because it showed serious damages due to heavy traffic loads and deicing salts. First, the conditions of deterioration in the cutting cross section and the lower surface of specimens sampled from the decks were observed. Then, the relationship between the degradation of resonant frequency at respective point of specimen and the fatigue process by wheel load trucking test was investigated. As a result, it was revealed that the decline of resonance frequency could make it possible to evaluate fatigue damage levels depending on internal cracks of bridge deck.