Bi2O3-B2O3-Yb2O3 system was investigated to determine the conditions of creation, melting character of ternary oxide phases and to find out the regions of glass-formation on the base of initial components. The investigations were carried out by the methods of physico-chemical analysis, DTA, RFA, IR-spectroscopy and density-measurements of Bi2O3×3B2O3-Yb2O3×B2O3; 3Bi2O3×5B2O3-Yb2O3×B2O3; Bi2O3×B2O3 Yb2O3×B2O3; 2Bi2O3×B2O3 - Yb2O3×B2O3 cuts. The chemically pure reactive: H3BO3; Yb2O3 and Bi2O3 were used as initial materials. The glasses of Bi2O3-B2O3-Yb2O3 system were boiled at 1000-1150 0C during 6-7 hours. After boiling the melt was poured out on titanium plate, which had room temperature. In dependence on composition the melt was cooled in form of transparent glasses, glass-crystals and crystals. On the base of these data about the character of specimens and by means of roentgen-study of obtained samples we determined the boundaries of glass-formation regions in Bi2O3-B2O3-Yb2O3 system. In Bi2O3-B2O3-Yb2O3 system the glass-formation region is tapered in Bi2O3×B2O3-Yb2O3×B2O3 cut, but in 2 Bi2O3×B2O3-Yb2O3×B2O3 cut at compositions from 10 mol % Bi2O3 to 40 mol % Bi2O3 the glasses with decreased thermal characteristics were revealed (Tmelt=3800C; Tcr=4400C). The synthesis of Bi2O3×B2O3-Lu2O3×B2O3, Lu2O3×B2O3-Bi2O3, Lu2O3×B2O3-Lu2O3×Bi2O3, Bi2O3×B2O3-Lu2O3×Bi2O3 systems was carried out by solid-state-phase method. Weighed according to calculation oxides were mixed, powdered and pressed to tablets. Obtained tablets were conglomerated at 9000C and then were thermally treated at 730-10000C in dependence on the composition. Preparated specimens were investigated by the methods of roentgenographyc analysis, IR-spectroscopy and density-measurements. The color of specimens was varied from brightly-yellow to brown. In Lu2O3-B2O3-Bi2O3 system three regions were revealed: homogenous glasses, crystal compounds and unmixed phases. The boundaries of regions of glass-formation were determined by visually and from roentgenographyc study of obtained specimens. Homogeneous glasses were obtained in follow cuts: Bi2O3×B2O3 - Lu2O3×B2O3 up to 15 mol % Lu2O3; Lu2O3×B2O3-Bi2O3 up to 10 mol % Lu2O3; Bi2O3×B2O3 Lu2O3×Bi2O3 up to 15 mol % Lu2O3. Polymorphic modifications are characteristical for the compounds of LnBO3-type (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu). Thermodynamical properties and heat capacity of these compounds are unstudied. Data about limits of solubility of components in Ln¢BO3-Ln¢¢BO3 systems (where Ln¢ and Ln¢¢ are various lantanoides) were not found. Variety of approximated equations Cp= f(T) have been determined by us for low-temperature modifications of L-LnBO3- type compounds. Maer-Kelli correlations: Cp=a+bT+cT-2 and values of heat capacity of B2O3, Ln2O3 binary oxides have been used for calculations.