This study developed mathematic models to convert ultraviolet-visible absorbance (UV/Vis) of bio-solublized coal to conversion ratios. By a mathematic regression method, the results showed that they had strong linear relationships. The highest correlation coefficient (0.99531) of the linear relationship between UV/Vis absorbance and coal bio-solubilization ratios was obtained at the wavelength of 513 nm. The high correlation coefficient further indicated that the use of UV/Vis with the proposed mathematic model would be an easier, quicker, and more accurate measurement, as compared with the conventional measurement of weighing coal loss after bio-solubilization.