The crystal structure and the dielectric properties of (1-x)Pb(Yb1/2Nb1/2)O3-xPb(Sc1/2Nb1/2)O-3 (PYN1- xPSNx) (0less than or equal to x less than or equal to 0.50) solid solution have been studied. According to our XRD study, the room temperatures crystal structure of PYN1- xPSN(x) becomes pseudocubic from the PYN's orthothombic with increasing x. Also the diffraction line intensities ascribed respectively to the AFE lattice modulation and the B-site ordering become gradually weaker and they disappear altogether for x > 0.30. In the PYN-rich composition range (0 less than or equal to x less than or equal to 0.30), the paraelectric(PE)-antiferroelectric(AFE) phase transition occurs sharply and is independent of the applied frequency. However, on further increasing Sc concentration (0.30 < x <= 0.50), the dielectric constant vs. temperature curve becomes gradually broader and begins to display a frequency-dependent relaxor behavior.