Four water-soluble dendritic phosphonated Ligands were first synthesized based on poly(amidoamine) (PAMAM) (generation 3 with 32 cascade end groups), with the hydrophilic amine or sulfonic acid groups on the surface of the dendrimer. Their Rh(I) complexes were used as the catalysts in the two-phase hydroformylation of styrene and 1-octene at mild reaction conditions. The results showed that these new water-soluble dendritic catalysts exhibited high catalytic activity both for 1-octene and styrene. These new catalysts also exhibited high selectivity for the iso-aromatic aldehyde, while in the long chain olefin case the selectivity was benefited for normal aldehyde.