Novel hyperbranched poly(triazene ester)s have been synthesized. These polymers represent a class of polymers with photo- and thermally labile moieties in each repeating unit. For the synthesis suitable AB(2) monomers containing these labile units have been designed. The polyesterification was performed at room temperature using 4-(dimethylamino)pyridinium 4-tosylate (DPTS) as catalyst and diisopropylcarbodiimide (DiPC) as activating agent. The polymers have been characterized by FAB-MS, SEC, DSC and H-1/C-13 NMR spectroscopy. The degree of branching was determined by quantitative high resolution C-13 NMR experiments and found to be 0.5. The thermal and photochemical stability of this polytriazenes has been investigated by UV/VIS spectroscopy and thermogravimetric analysis.