Cryogenic STM/STS experiments of heavily Pb‐doped Bi2Sr2Ca2CuOy(Bi2212) superconductors were performed at 4.3 K. We succeeded in observing various kinds of atomic impurities as well as nano‐scale inhomogeneity of energy gap widely seen in Bi‐based superconductors. Furthermore, we found that the distribution patterns of impurities are not correlated with the spatial map of gap values derived from STS spectra, implying that the electronic inhomogeneity is not a consequence of the randomly distributed impurity atoms. These results strongly suggest that the inhomogeneity originates from atomic‐scale disorder of excess oxygen which is invisible by STM. © 2003 American Institute of Physics