The solubilities of 9H-fluoren-9-one and dibenzo[b,d]furan in ethanol, butan-1-ol, ethyl ethanoate, methylbenzene, 2-isopropoxypropane, and tetrachloromethane were measured using the isothermal method from (283.15 to 333.15) K. The experimental data were then correlated with the Apelblat equation, and the activity coefficients were correlated using the Scatchard-Hildebrand regular solution equation and nonrandom two-liquid (NRTL) equation. Besides, ternary phase diagrams of 9H-fluoren-9-one + dibenzo[b,d]furan + ethanol, 9H-fluoren-9-one + 9H-fluorene + ethanol, and 9H-fluoren-9-one + 1,2-dihydroacenaphthylene + ethanol were also presented. The results show that all systems were simple eutectic systems, and the significant change of solubility in 9H-fluoren-9-one + dibenzo[b,d]furan + ethanol system can be attributed to the intermolecular forces between dibenzo[b,d]furan and 9H-fluoren-9-one.