The influence of mole fraction and nature of the cations in positions [8]A and [6]B of the pyrochlores containing Na+, Ca2+, Cd2+, U4+, Nb5+, Ta5+, Ti4+, Sb5+, Zr4+, V3+, V4+, W5+, W6+ synthesized under hydrothermal conditions at 800 °C, 200 MPa and controlled oxygen fugacity in NaF solution of 1.0 mol·kg−1 H2O on lattice parameters has been considered. The unit cell parameters of the fluorpyrochlores where for Nb5+ or Ta5+ were substituted by other cations showing distinct linear variations from the effective cations radii in positions [8]A and [6]B. Based on the literary data analysis, the two-parameter nonlinear equation describing dependence of pyrochlore lattice parameters on the cation radii for the oxide-pyrochlores has been proposed. [ABSTRACT FROM AUTHOR]