Pb(1-x)Lax [(Zr0.6Ti0.4)(1-x)(Mn1/3Sb2/3)x]O3 ceramics with x = 0.02, 0.03, 0.04, and 0.05 were synthesized by using a conventional solid state reaction route. The influence of La, Mn, and Sb contents on phase structure, microstructure, and electric properties were investigated. The results of X-ray diffraction (XRD) show that the phase structure of the ceramics transforms from rhombohedral phase to tetragonal phase. However, the minority pyrochlore phase appears on the micrographs of XRD and SEM if the doping concentration is greater than 2 mol%. The grain size of the ceramics gradually increases (from 1.36 μm to 1.57 μm) with increasing doping. The dielectric properties of the ceramics have been measured as a function of temperature in the range of 20 °C to 430 °C at 1 kHz. The results indicate that the transition temperature and the maximum dielectric constant decrease with increasing PL-PMS content in the system. These results clearly show the significance of PL-PMS in controlling the dielectric behavior of the PL-PMS-PZT system.