Abstract: The block copolymerization and structure of the copolymer of polyethylene oxide)(PEO)with sodium methacrylic acid(NaMAA)were studied respectively.The ultrasonic copolymerization in PEO-PNaMAAaqueous solution follows the kinetic relationship,-d[M]/dt=k[R]^1/6[M].With increasing irradiation time or monomer concentration,the yield and NaMAAcontent in the block copolymer are increased.The chemical and morphological structure of the copolymer were identified by IR,MS,NMR,TEM,DSCetc.,and the results showed that the copolymer obtained was a block one.The yield of the copolymer,formed by irradiating1% PEO-10% NaMAAaqueous solution for a period of 15 min.at 21.5 kHz with 0.7Acathode current,was 24.0%.