The present invention provides an insulating coating treatment solution capable of forming a chromium-free insulating coating excellent in moisture absorption resistance, capable of imparting high tension, and excellent in reducing iron loss, and capable of suppressing the occurrence of coating unevenness when coating a steel plate. resulting in poor appearance. The insulating coating treatment solution is used to form a chromium-free insulating coating on the surface of the grain-oriented electrical steel sheet, and the insulating coating treatment solution contains: one of the phosphates selected from Mg, Ca, Ba, Sr, Zn, Al, and Mn or two or more phosphates; colloidal silica; and particles of compounds containing metal elements, with respect to 100 parts by mass of the phosphate, the content of the colloidal silica is expressed as SiO 2 The solid content is 50 to 120 parts by mass in terms of solid content, and the content of the particles of the compound containing metal elements is 5 to 60 parts by mass in terms of metal elements, and the thixotropic index (TI) of the insulating coating treatment solution is 1.00 Above and below 10.00.