The highly reactive water-soluble hydroformylation catalyst, rhodium polyethylene glycolate (Rh(PEG),), prepared by the reaction of polyethylene glycol and rhodium trichloride hydrate, was used as a catalyst for hydroformylation reactions of olefins, such as dodec-1-ene, 2.4.4-trimethylpent-1-ene and styrene, in biphasic systems. The reactions were done in a broad temperature range and at a pressure range from 7 to 12 MPa. Turnover frequency for the catalytic reaction of the low reactive 2.4.4-trimethylpent-1-ene is 450 (mol aldehyde/mol Rh x h), which is 3 times higher than in comparable homogeneous rhodium systems. The selectivity for aldehydes is excellent(> 98%). The dependence of the conversion vs. time was monitored for different partial pressures, pH values, temperatures and catalyst concentrations. Activation parameters have been calculated for the hydroformylation of the olefins in water and polyethylene glycol with rhodium polyethylene glycolate as a precatalyst. The activation energy in water is calculated for the hydroformylation of various olefins (dodec-1-ene E-a 95 kJ/mol, 2.3.3-trimethylpent-1-ene E-a 30 kJ/mol and styrene E-a 33.1 kJ/mol). The hydroformylation reaction with rhodium polyethylene glycolate as a precatalyst is first-order for dodec-1-ene and 2,4,4-trimethylpent-1-ene and zero-order for styrene.