The anomalous behavior in the temperature dependence of ESR spectra has been discovered for the powder sample and LB film of poly[5-(acrylamidophenyl)-10,15,20-triphenylporphyrinato]silver(II) (denoted by polyAgAATPP) under oxygen atmosphere. The ESR intensity decreased with the decrease of temperature from room temperature to -150 degrees C. The IR and Raman spectroscopies at liquid nitrogen temperature revealed that the new IR-and Raman-active peaks appeared at 782 and 545 cm(-1) for the LB film of polyAgAATPP under oxygen atmosphere, respectively. The peaks were assigned to v(O-O) and v(Ag-O) in the dioxygen adduct of polyAgAATPP, respectively. The linkage between AgTPP moieties and dioxygen was likely to be of the bridging type. These phenomena were not observed for monomeric AgAATPP.