The stress corrosion cracking (SCC) behavior near the fusion boundary (FB) of a dissimilar weld joint with Alloy 182-A533B low alloy steel (LAS) in high-temperature oxygenated water doped with sulfate has been investigated, with a focus on the relationship between the SCC crack arrest/reinitiation behavior and the microstructural characteristics of the heat-affected zone (HAZ) in LAS adjacent to the FB. Cracks propagated perpendicular to the FB along the dendrite grain boundary in the dilution zone (DZ) of Alloy 182, and then spherical or crack-like oxides were formed in the HAZ of LAS adjacent to the FB; no obvious SCC susceptibility was observed in the non-HAZ region of LAS. Crack arrest occurred when spherical oxides formed in the LAS. Crack-like oxides tended to propagate along the prior austenite grain boundary in the coarse-grained HAZ (CGHAZ) of LAS. It has been suggested that the microstructure and continuity between the dendritic grain boundary in the DZ of Alloy 182 and the prior austenite grain boundary in the CGHAZ of LAS across the FB, that is, the continuity of the potential crack path played an important role in the arrest/reinitiation of SCC crack in the FB region. Above microstructural characteristics varied depending on the multiple heat cycles of the welding process.