The phase structure, dielectric, ferroelectric, and piezoelectric properties of (1-2x)BiScO3-xPbTiO(3)-xPbMg(1/3)Nb(2/3)O(3) ceramics (x = 0.30-0.46) were studied. It was found that an increase in x leads to a structural phase transition between the rhombohedral and tetragonal phase via an intermediate monoclinic phase and to a crossover from the nonergodic relaxor state to the ferroelectric one. It was proposed that at x > 0.42 the phase transition changes from second to first order. The assumption about the existence of a tricritical point on the phase diagram at x approximate to 0.42 with the enhanced dielectric response has been made. The observed structure-property relationships of the studied solid solutions are discussed. It is shown that the solid solutions with x = 0.42 are characterized by the high piezoelectric parameters (d(33) = 509 pC/N, d(31) = -178 pC/N, d(h) = 153 pC/N), which makes possible their applications in sonar equipment.