Abstract: The hot dip Al-Zn layer was passivated with La(NO3)3-doped BTESPT solution in which the layer was dipped at 25°C and cured at 120°C for 30 min, thus forming a passive film on the layer. The structure, surface morphology and corrodibility of the substrate after passivation were studied experimentally. FTIR (Fourier transformation infra-red spectroscopy) showed that the La(NO3)3-doped BTESPT films have been successfully deposited by chemical bonding between the solution and hot dip Al-Zn substrate and by the formation of SiOAl and SiOZn. No obvious difference is found between the components of major organic groups in the passive films deposited and the undoped BTESPT films. SEM results indicated that the films deposited are compact and homogeneous without clear tiny cracks. The EDS (energy dispersive spectrometry) results showed that the films consist mainly of such elements as C, O, Si, S, Al, Zn and La. The test results of corrosion resistance showed that the corrosion potential and current density of the passive films decrease obviously, while the polarization resistance increases. It is therefore proved that the passivisity by La(NO3)3-doped BTESPT is much higher than that without doping in regard to corrosion resistance.