Temperature dependent dielectric behavior of sol-gel derived ferroelectric Pb1−xLaxTiO3 (PLT) (x = 0.05 to 0.30) thin films on Pt/Si substrates has been studied. The characteristics of the diffuse phase transition and possible relaxor behavior of PbTiO3 thin films doped with different amounts of La are investigated. Room temperature X-ray and micro Raman results indicate that the crystal structure of the PLT films was strongly influenced by the La content. The softening of the E(1TO) mode with increasing La content indicates that the incorporation of La in the PT lattice results in a structural disorder in the material. The dielectric permittivity and loss tangent of the PLT thin films were measured in the temperature range of 80 –700 K at frequencies between 1 kHz and 1 MHz. Transition temperatures (Tm) for PLT (x = 0.05, 0.20, and 0.30) are 640, 460, and 254 K respectively, and are higher in comparison to reported values of bulk ceramics. The permittivity maximum broadened, and showed relaxor- type frequency dependent permittivity characteristics for PLT (x = 0.30) films. The broadening parameter was significantly influenced by La doping and our results indicate that PLT thin films undergo a normal-to-relaxor ferroelectric transformation for La concentrations of 25 at% in PLT films.