Dielectrical property on poly(methacrylic acid-ethylene glycol dimethacrylate) P(MAA-EDMA)] attached with nanosized CdS particles have been studied. The attachment of CdS nanoparticles alters the dielectric property of CdS-P(MAAEDMA) samples. By addition of a certain amount of CdS nanoparticles, the dielectric constant at room temperature and 100 Hz of the CdS-P(MAA-EDMA) is enhanced by ca. 500 times, which is attributed to the interfacial interaction of CdS nanoparticles with polymer surface. The large value of dielectric constant is due to interfacial space charge polarization.