Abstract: A method of producing tricyclodecane dicarbaldehyde and/or pentacyclopentadecane dicarbaldehyde by the hydroformylation of dicyclopentadiene and/or tricyclopentadiene. The tricyclodecane dicarbaldehyde and/or pentacyclopentadecane dicarbaldehyde in the hydroformylation product liquid are extracted with an extraction solvent comprising a polyhydric alcohol having 2 to 6 carbon atoms. With such extraction, the tricyclodecane dicarbaldehyde and/or pentacyclopentadecane dicarbaldehyde transfer into the extraction solvent while retaining the catalyst components in the hydroformylation solvent. The controlled extraction atmosphere with an oxygen concentration of 1000 ppm or lower prevents the rhodium compound from transferring into the extraction solvent, thereby avoiding the loss of expensive rhodium.