Electron probe microanalysis (EPMA) on F82H heats revealed microsegregation of at least four metallic elements, including chromium, tungsten, vanadium, and manganese. Segregation of these elements was observed as a band-like structure parallel to the rolling direction. The maximum difference in tungsten content due to the tungsten segregation was about 1.0wt.% between the bands. This difference in the tungsten content affected the tungsten contents in both the matrix and precipitates. In particular, precipitation morphology was affected after aging at 923K for 2000h. Laves phase, (Fe, Cr)2W, precipitated along tungsten-enriched bands in the aged specimen. Consequently, these aligned Laves phases decreased USE (upper shelf energy) by about 20% for the Charpy specimens with a V-notch parallel to the segregation band. Thus, we also tried to find appropriate homogenizing conditions to diminish such microsegregation and suggested the condition of 144h at 1453K. This condition did not form δ-ferrite, which is known to be a phase harmful to material toughness.