The role of a highly crystalline and oriented lead titanate (PTO) seed layer on the subsequent phase and texture evolution of lead zirconate titanate (PZT) thin films is investigated in situ using X-ray diffraction (XRD) during crystallization. Crystalline PTO seed layers were first prepared via a 2-methoxyethanol route. Amorphous PZT with a Zr/Ti ratio of 52/48 was then deposited on the seed layer using the same synthesis route and subsequently crystallized in situ during XRD. During heating, a tetragonal-to-cubic transformation of the seed layer occurs prior to the formation of perovskite PZT. Subsequent nucleation of the crystalline PZT occurs in the cubic phase. Simultaneous to nucleation of PZT, development of a dominant 100 texture component was observed in the PZT phase of the thin films. The results indicate that 100 textured PTO nucleates 100 texture of PZT thin films during crystallization.