The liquid-liquid biphasic thermomorphic or temperature dependent multicomponent solvent (TMS) is an attractive alternative to the conventional single or biphasic reaction media system. In such a solvent, the catalyst remains as a residue in one of the liquid phases and the product goes preferably to the other liquid phase providing ease of product separation and catalyst recovery. This paper describes the kinetics of hydroformylation of two higher olefins (1-octene and 1-dodecene) using a homogeneous catalyst consisting of HRh(PPh3)3(CO) and P(OPh)3 in a TMS- system containing propylene carbonate (PC), dodecane and 1,4-dioxane. The effect of concentration of the olefins, catalyst loading, partial pressure of CO and H2 and temperature on the rate of reaction has been studied at temperature of 353, 363 and 373 K. The rate was found to be first order with respect to catalyst, 1-octene and partial pressure of H3. The rate vs. PCO shows a typical case of substrate inhibited kinetics. Three generalized rate models were developed on the basis of plausible reaction pathways. The kinetic and equilibrium parameters of the models were estimated by nonlinear least square regression of experimental data. Conventional model discrimination techniques were used to identify the correct one. The rate model with H3-addition as the controlling step was found to represent the rate data. The rate model predicted the conversion of the two alkenes satisfactorily with an average absolute error of ±4.0 .