Crystalline-like substances observed on the surfaces of oil paintings were analyzed by an electron probe x-ray microanalyzer (EPMA) and an x-ray microdiffractometer (MDG). The samples were taken from Hazama's oil painting Shakuyaku (Peony). By an EPMA, three combinations of elements were observed: type 1 was zinc and sulfur, type 2 was zinc, potassium and sulfur, and type 3 was zinc, potassium, magnesium and sulfur. By an MDG, ZnSO₄.6H₂O was identified for type 1 and (NH₄)₂Zn(SO₄)₂.6H₂O was identified for type 3. Three other different diffraction patterns were observed for types 2 and 3, but no corresponding compounds were found. These results indicate the samples to be some complex compounds of zinc, potassium and sulfur for type 2 and zinc, potassium, magnesium and sulfur for type 3. Cross-sections of paint fragments and grounds of the work were analyzed by an EPMA and an MDG. The results of these analyses showed that there were no crystalline-like substances in the painting layers and grounds, but sulfur was detected from the surface of grounds. These results indicate the possibility that the work was affected by SO₂ gas. It was considered that the crystalline-like substances were the results of blooming.