The hydroformylation of olefins using Rh(acac)(CO)(2) as a catalyst with the excess of PPh3 was investigated at the temperature of 80 degrees C within the pressure range from 4 to 12 bar in a neat substrate, without a solvent. The conversion of 1-hexene was complete, with a linear-to-branched aldehyde ratio of ca. 10. Very good results were also obtained for 1-pentene and 1-octene. The catalytic performance of the Rh(acac)(CO)(2)/PPh3 catalytic system in hydroformylation under solventless conditions was better than that in toluene, owing to the high concentration of the reactants. Recycling experiments confirmed the good stability of the catalyst and its constant activity. (C) 2015 Elsevier B.V. All rights reserved.