High molar mass Polyester Amide was obtained by coupling reaction of Carboxyl-Terminated Polyamide 12 (CTPA) with a dioxazoline (OO). The analysis of the experimental condition effects on the reaction conversion and the structure of the polymer obtained did not show any particular side reaction. A kinetic study comparing the reactivity of the dioxazoline used with CTPA and decanoic acid (DA) as model reactants showed the equireactivity of the two oxazoline functions and of the acid functions of the CTPA and DA. A kinetic model was proposed. The reaction rate at different temperatures and the activation energy were calculated. The evolution of the different reactant concentrations were modeled and compared with experimental data.