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 this time were taken from five paintings. The samples from three paintings showed nearly the same results as follows: Zn, Mg, and S (type 1) or Zn, Mg, K and S (type 2) were detected by EPMA; by MDG, MgSO₄.7H₂O was identified for type 1 samples and (NH₄)₂Zn(SO₄)₂.6H₂O was identified for type 2. An unidentified diffraction pattern was observed for both types. The samples from the fourth painting contained no element having atomic number greater than Ne, and the diffraction pattern was observed but not identified. By chemical microscopy, the samples dissolved to xylene. The samples from the fifth painting was identified as lead white. Considering these analytical results and those reported in previous papers, crystalline-like substance may be classified into three groups. The substances of group 1 contain sulfur and ammonium salt, and their appearance seems to be the result of a process of blooming similar to that which Thomson indicates in The Museum Environment. The substances of group 2 seem to be organic compounds such as solidified natural resin or oil which were contained in the paint layer. The substances of group three are the pigments which were taken from the surface paints that had flaked off due to a phenomenon like chalking. There was no damage caused by crystalline-like substances that appeared on the surfaces of oil paintings.