A varnish comprising a ground substance consisting of a polymer or oligomer of 200 to 50′104 molecular weight or organic compound of 200 to 1000 molecular weight and a solvent containing a good solvent and a poor solvent whose boiling point (under 760 mmHg) is at least 20° C. lower than that of the good solvent, wherein the ground substance is dissolved in the solvent. Any thin film prepared from this varnish is substantially from generation of foreign matter, so that it can appropriately be used as thin films for electronic devices and those for use in other technical fields.