The decay of excited states in 255No was investigated by applying the evaporation-residue–conversion-electron correlation technique. Two new isomeric states were observed in 255No together with the previously known one. Excitation energies of the isomeric states were estimated based on the energies of conversion electrons and γ rays from correlation chains. These results were in accord with theoretical calculations based on the mean-field models. A tentative decay scheme of isomeric states in 255No is proposed, and their Nilsson configurations are discussed. The energy decrease of the 11/2−[725] Nilsson level for heavy N=153 isotones as a function of increasing proton number is confirmed.