Nanocrystalline PLZT thin films of composition Pb1-xLaxZr0.52Ti0.48 (x = 0, 2, 5%) were deposited on silicon substrates by sol-gel process using lead acetate trihydrate, lanthanum nitrate hydrate, zirconium propoxide and titanium propoxide as lead, lanthanum, zirconium and titanium precursor materials. Experimental studies have been made on solitary waves in 2 mol% lanthanum doped sol-gel derived lead zirconate titanate thin films. The solitary waves are generated under the influence of external alternating electric field, which has the same frequency as the external field. These solitary waves propagate through the thin film upto its boundary and then reflect back. The magnitude of the solitary waves attenuates as they move away from the electrodes and their phase reverses on reflection. For certain frequencies of the external electric field, solitary waves exhibit resonance effect. Distortion in hysteresis loops has been demonstrated on the basis of solitary waves propagation in the film having different electrode area.