Provided are a composite for forming a ferroelectric thin film which is a colloidal solution applicable to the MOD method and capable of maintaining excellent dispersion stability and preservation stability of an organometallic compound over a long term, a ferroelectric thin film, a method of manufacturing a ferroelectric thin film, and a liquid-jet head. A composite for forming a ferroelectric thin film, which is made of a colloidal solution applicable to the MOD method containing an organometallic compound including metal constituting a ferroelectric thin film, and contains water other than water of crystallization in the organometallic compound is used when forming a ferroelectric thin film in accordance with the MOD method.