Abstract: Based on the results of other researchers on the corrosion rate of tensile reinforcement steel, moment resistance deterioration models of reinforced concrete girder bridges due to steel corrosion induced by chloride attack or concrete carbonation are developed with pitting corrosion being considered for chloride attack and average corrosion being considered for concrete carbonation. A computer program for time- dependent reliability assessment of highway concrete bridges based on Monte Carlo method and statistic regression is also developed. A concrete girder bridge in Beijing area is taken as an example. The results show that the ultimate limit state reliability of the bridge due to chloride attack reduces to the design target reliability at the 30th year or so and the reliability due to concrete carbonation to the value at the 50th year or so. Therefore, the bridge can not work through the presumed working life of 100 years without major repair. The results also show that cracking time of concrete cover induced by corrosion of tensile reinforcement is much earlier than the time when the ultimate limit state reliability reduces to the target value. This is important for bridge inspection/repair schedule.