Active radicals formed during the sonolysis of PVK (polyvinyl carbazole) and PMMA (polymethylmethacrylate) have been studied with the combination of spin thepping technique and ESR spectroscopy-The results show that: 1. For PVK, radicals CA and--CH_2--CH--are produced during the ultrasonic irradiationand only the later can be trapped by MNP. 2. For PMMA, radicals --C and --CH_2 are grnerated by sonolysis and both can be trappedby ND. Active radicals formed during the sonolysis of PVK (polyvinyl carbazole) and PMMA (polymethylmethacrylate) have been studied with the combination of spin thepping technique and ESR spectroscopy - The results show that: 1. For PVK, radicals CA and - CH_2 - CH - produced produced during the ultrasonic irradiation and only the later can be trapped by MNP. 2. For PMMA, radicals - C and - CH_2 are grnerated by sonolysis and both can be trapped by ND.