PURPOSE: To improve the completion of the reaction and obtain a product layer selectively by the oxo reaction of a bridged alicyclic nonconjugated diolefin, etc. to obtain a polycyclic diol, by using a reactor consisting of two reaction chambers of a rising current part and a descending current part.

CONSTITUTION: A bridged alicyclic compound having two double bonds or one double bond and one formyl or OH on the one side and the other side with a bridge- head carbon placed therebetween is reacted with CO and H2 in the presence of cobalt carbonyl and an organic tertiary phosphine as catalysts in a nonpolar solvent at 160W220°C and 50W200kg/cm2 G to give a polycyclic diol. In the process, a partition plate is provided in a reaction vessel 1 to divide the first reaction chamber 3 from the second reaction chamber 4, and the bridged alicyclic compound, CO, H2 and the nonpolar solvent containing the catalyst are fed from the bottom of the first reaction chamber 3. The resultant polycyclic diol 6 after the phase separation is taken out of the bottom 7 of the second reaction chamber 4. The consumption of the raw materials and energy can be reduced.