Post irradiation examinations (PIEs) of Zry-2 cladding and spacer specimens irradiated for 5 cycles in a Japanese commercial boiling-water reactor (BWR) were performed, and were investigated regarding the mechanism for the local increment of corrosion and hydrogen absorption. We conducted transmission electron microscopy (TEM) observations and electrochemical (EC) measurements of these samples. Based on the results of TEM observations of the microstructure in the 5-cycle irradiated cladding specimens with lower Fe and Si content, the following distinguishing properties were observed relative to cladding specimens with more usual corrosion properties: 1) existence of high density microcracks and pores near the oxide/matrix (O/M) interface, 2) disappearance of tetragonal phase zirconium oxide (t-ZrO2) on the matrix with an accumulation of zirconium hydride (ZrH1.6), 3) a decreasing trend of the number density of second phase particles (SPPs). Furthermore, based on the EC measurements, it was observed that the flat-band potential decreases with increases in the fast neutron fluence. In this paper, we will explain the mechanism of corrosion in high burnup region based on these examination results.