There are many kinds of uncertainties involved in the evaluation of corrosion process and deterioration of structural performance. Because of the presence of uncertainties, it is necessary that long-term structural performance be treated based on reliability concepts and methods. This paper presents a probabilistic framework for estimating the time-dependent reliability for existing prestressed concrete structures in a marine environment based on a non-linear filtering technique denoted Sequential Monte Carlo Simulation (SMCS). The results of manual measurement or automatic monitoring are used as observational information. The emphasis is placed on investigating the effects of the differences between manual measurement and automatic monitoring, and possible interruption periods of health monitoring on updated estimates of reliability of prestressed concrete bridges located in a marine environment.