Preparation technology for monophase Li1–у[Nb1-xTax]1+уO3 compounds nanoparticles with different but predictable (unlike the crystals growth technology) chemical compositions via mechanosynthesis method have been developed. This opens a way for the investigation and clear establishment of their changes connected with properties dependencies on x value and Li/(Nb1-x+Tax) ratio. Such investigations are important in terms of studying the physico-chemical processes, that accompany the formation of either nanocrystalites themselves or powders and ceramics based on them as precursors for their monocrystals further growth. Besides, the synthesis of new compounds Li1–у[Nb1-xTax]1+уO3 in the form of nanoparticles, that are applied for the creation of piezoelectric elements, biomarkers, generation of higher harmonics of laser radiation, preparation of hybrid photoelectric, electrooptical and pyroelectric materials (the incorporation of LN, LT or LN-LT nanoparticles into the polymeric matrices), fabrication of ceramics based on nanopowders, etc., is interesting by itself. Structural, optical and electrophysical methods of research are widely used for LN and LT nanoparticles, powders and ceramics based on them. But in each paper, some research methods are applied for specific materials compositions. At the same time the comprehensive research of nanoparticles, nanopowders and nanoceramics with the simultaneous use of X-ray diffraction, impedance spectroscopy, Raman spectroscopy, diffusing-wave spectroscopy, microscopy methods for pure LN and LT, as well as for the series of mixed compounds Li1–у[Nb1-xTax]1+уO3, is unknown for us. So, comprehensive investigations dealing with establishing dependencies of structural, electrophysical and optical properties of stoichiometric and nonstoichiometric nanocrystalline compounds LiNb1-xTaxO3 were obtained using mechanosynthesis method, on the degree of substitution x will be discussed.