Potassium-modified polycrystalline samples of PLZT, Pb-0.91(La1 - z/3Kz)(0.09)(Zr0.65Ti0.35)(0.9775)O-3 [z = 0.0, 0.1, 0.3, 0.5, 0.7], were prepared using sol-gel technique. X-ray diffraction (XRD) of these compounds show that they can be formed in single phase at 800 degrees C. Pellets prepared from the above powders were sintered at 1100 degrees C. Detailed studies of the dielectric constant (epsilon) and loss tangent (tan delta) of the compounds at different frequencies (400 Hz to 10 kHz) at room temperature (RT) and temperature (RT to 350 degrees C) suggest that the compounds undergo ferroelectric phase transition of diffuse-type on increasing K-concentration. Analysis of diffuseness of these compounds gives a value close to 2, which indicates the presence of higher degree of disorder in PLZT substituted by K. The dielectric constant (epsilon) is found to increase initially and then to decrease with increasing K concentration.