The influence of ultrasound irradiation on the 3,8,13,18-tetramethyl- 21H, 23H- porphine- 2,7,12,17 tetrapropionic acid, or Coproporphyrin-I (CPI), was examined by means of a sonicator with a “cup horn”, thermostatted at 20 or 40 ± 1⁰C. After each sonication, the solutions were periodically analysed by an UV-VIS spectrophotometer and pH meter. The identification and characterization of the sonication products has been performed by electrospray mass-spectrometry (ESI-MS). Different initial conditions of pH and sonication have given: the degradation of the CPI molecule, the formation of a CPI-N-oxide and CPI-N-N’-dioxide or not any modification.