Photo decomposition and stability under acidic conditions were studied for photo base generators (PBGs) having a borate anion. Borate-type PBGs were unstable under acetic acid conditions and quickly decomposed. However, PBGs bearing electron-withdrawing groups on an aromatic ring of borate showed good stability. According to HOMO-LUMO energy calculated basis at the B3LYP/6-31G(d) level, PBGs that had lower HOMO levels showed higher stability. Photolysis of PBGs was also studied and free energy changes estimated based on the Rhem-Weller equation. A higher stability was observed under acidic conditions co-existing with a sensitizer. When PBGs were evaluated in a system consisting of epoxy resin, carboxylic oligomer, sensitizer and an m-fluorinated aromatic ring on borate, it showed good potential for use in photoresists.