To provide a method for forming a thin film, which consist of a metal complex useful as a light emitting element, is very thin and has high stability and high molecular density, is excellent in thickness precision, simplicity and certainty.

The method for forming the thin film consisting of the metal complex on a base material is constituted of (1) a first process in which the base material having a surface made of a metal oxide is dipped into a solution containing the metal complex having at least 2 or 3 ligands and a metal in the molecule and having the structure in which 2 to 8 groups among phosphoric acid group, phosphonic acid group and their derivative groups are bound to the ligand in one molecule thereof, (2) a second process in which excess metal complex not chemically absorbed on the base material surface is removed and then the base material is dried, (3) a third process in which the base material is dipped into an aqueous solution of a salt of a metal belonging to the group IV of the periodic table, (4) a fourth process in which the base material is water-washed and then is dried, and (5) a fifth process in which the base material obtained by the fourth process is subjected to a treatment of from the first process till the fourth process at least one more time.