To clear chemical forms of boron in coals and its origin, specific gravity separation tests for 4 coal samples were performed, and the boron concentration in each sample was measured. The boron concentration in coal has a high positive correlation with the vitrinite content in coal. Other maceral, exinite containing a large amount of resinite, indicates extremely low boron concentration. It is found that the boron concentration in coal decreases with increase of resinite content. In minerals such as quartz, kaolinite, montmollironite, illite, dolomite, and calcite, illite contains the highest concentration of boron. However, the boron concentration of illite does not affect on that of coal, because illite content in coals is very little (bellow about 1%). Since the boron concentration in minerals is low, consequently, it is difficult to remove boron in coal by the deashing operation. The origin and the chemical form of boron are discussed. It is seemed that boron in coal is consisted by water-soluble compounds and water-insoluble compounds. As the water-soluble compound, it is estimated some compounds such as boric acid and borate originated from immersion of seawater or ground water and biogenic fixation by plants. The water-insoluble compounds will probably borosilicate originated from flowing into sedimentary layer with ground water or seawater.