The microstructure of the highTcphase (Tc∼111 K) in the Sb‐Pb‐Bi‐Sr‐Ca‐Cu‐O system has been determined using transmission electron microscopy. Its crystal structure belongs to the superspace groupNBbmb11¯1, NBb2b111,PBbmb11¯1orPBb2b111with subcell lattice parametersa=5.411(1) A˚,b=5.411(1) A˚, andc=37.22(6) A˚. The highTcphase has a modulated structure withb‐axis wavelengths 26.9 and 36.1 A˚. Stacking faults along thecaxis in the highTcphase are much less numerous than in the Bi‐Sr‐Ca‐Cu‐O system, but comparable to the Pb‐Bi‐Sr‐Ca‐Cu‐O system. Sb substitution for Ca may affect the internal strain of the crystal.