Compact swelling in Pb‐doped Bi‐Sr‐Ca‐Cu‐O superconductor has been studied by observing the effects of the size of calcined powders, volatilization of materials, and sintering of high‐Tc(2223) powders. The bulk density increases at the early stage of sintering, for about 20 h, and then decreases. Densification occurs when the low‐Tc(2212) phase and a liquid phase exist, whereas dedensification occurs with the formation of the 2223 phase regardless of the presence of the liquid. Gas evolution from specimens does not appear to be responsible for compact swelling. Compact swelling is explained by anisotropic growth of thin, platelike 2223 grains in random orientation. When 2223 grains grow in a preferred direction, compact swelling