This paper discusses the capability of Eddy Current Monitoring (ECM) system as a in-situ evaluation method of crack propagation in a Boiling Water Reactor (BWR) environment. The ECM experiment with the eddy current probes on the outer surface of a large-scale pipe specimen, demonstrates the capability to monitor the propagation of cracks introduced from the inner surface of the specimen in a simulated BWR environment. The numerical simulation of eddy current signals shows that the experimental signals can explain the crack propagation. This provides that the ECM system is an effective method to evaluate the crack growth quantitatively.