In this paper, we report on novel Rh/phosphonate-phosphine catalysts for the aqueous two-phase hydroformylation of long-chain olefins. The amphiphilic ligands Ph2P-(CH2)(10)-PO3Na2 and Ph2P-(CH2)(12)-PO3Na2 have been shown to form Rh catalysts that are superior to Rh/TPPTS systems. Aldehyde selectivities higher than 95% and high activities (e.g., TOF of 660 h(-1) at 88% yield) were achieved. Counterions such as Na+, K+, NH4+, and NH3Pr+ influence the catalyst retention, whereas the lowest rhodium losses into the organic phase were found with a sodium phosphonate ligand. Phase separation by simple decantation was accelerated when methanol was added to the biphasic system.