A process for forming a functional ceramic thin film eliminating the need of high temperature annealing which has been indispensable in the conventional process is provided. This can be achieved by the process for forming a functional ceramic thin film having a crystal of a composite oxide consisting of two or more metal elements and oxygen, which comprises steps of alternately stacking seeding layers having the same crystalline structure as said composite oxide and formable at a temperature lower than the crystallization temperature of the composite oxide, and layers containing a larger amount of a specified metal element than said seeding layers, and then annealing the resultant layers to form an integral body.