Phase equilibria in the system (Bi1-xSbx)(8)Pb5O17 (x = 0-0.3) was studied using high temperature X-ray diffraction in combination with differential thermal analysis. Five phases were identified in this system: tetragonal Bi8Pb5O17(beta(2)), tetragonal Bi1.23Pb0.77O2.62(beta(3)), intermediate Phi-phase, body-centred cubic Bi8Pb5O17(beta), and orthorhombic Bi3SbO7(chi); the temperatures at which these different phases occurred were thus determined. Of particular interest in relation to undoped Bi8Pb5O17, were the temperature ranges ton heating): below 420 degrees C, pure beta(2)-phase; 420-460 degrees C, coexistence of beta(2)-phase and Phi-phase; 460-590 degrees C, Phi-phase; 590-615 degrees C, a mixture of Phi-phase and beta-phase; above 615"C, pure beta-phase. On cooling, the high temperature beta-phase transfers to the beta(2)-phase in the temperature range 615-590 degrees C. Increasing the Sb concentration, x, in (BixSb1-x)(8)Pb5O17 caused a decrease in the temperature at which pure beta-phase formed on heating. At 10 mol% Sb dopant level, the Phi-phase appears at much lower temperatures than the others. Two hypothetical binary diagrams (of Bi8Pb5O17-Bi3SbO7) were constructed for heating and cooling regimes, respectively, which show the phases present in (BixSb1-x)(8)Pb5O17 over a range of different Sb concentrations (x = 0-0.3) and temperatures (room temperature to 630 degrees C).