Mass‐spectroscopic studies on biased laser ablation of Ba2Y1Cu3O7−&dgr;have been carried out by using time‐of‐flight mass‐spectroscopy. The energies of the ions were hardly influenced by the electric field created by substrate biasing. This is probably because the ions in the plume are shielded from the external electric field by electrons. Energy differences between the atomic, monoxide and cluster ions have been observed. While the former has an energy of about 200 eV or more, the latter two have only a few eV. This implies that atomic ions are accelerated during the initial laser ablation process and monoxide and cluster ions are produced through plasma reactions in the plume. The multi‐valenced ion species (Cu2+and Cu3+) were observed under positively biased conditions. They should be one of the key factors in preparing high quality superconductive thin films at lower deposition temperatures due to their high internal energies.