The quantitative analysis of Li content in the liquid-phase epitaxial (LPE) grown LiNb1-xTaxO3 (LNT) film by combining high-resolution X-ray diffractometry (HR-XRD) and electron probe microanalysis (EPMA) is proposed. The X-ray rocking curves of the LNT films grown on LiNbO3 (LN) substrates are simulated, and then the interface sharpness is analyzed. The combination of HR-XRD and EPMA reveals that the Li content in the LNT films increases with decreasing growth temperature. The simulation of rocking curves suggests that the LNT/LN films do not have the thick fluctuation layer in Li content, but they have Nb/Ta interdiffusion layers at the interfaces. The activation energy can be estimated from an Arrhenius plot of the calculated diffusion coefficients. (C) 2002 Elsevier Science B.V. All rights reserved.