An image forming system includes a sheet processing apparatus, a heat presser, an image forming apparatus, and control circuitry. The sheet processing apparatus separates a two-ply sheet in which two sheets are overlaid and bonded together at a portion of the two-ply sheet, and sandwiches a sheet medium between the sheets of the two-ply sheet. The heat presser heats and presses the two-ply sheet. The control circuitry performs a first mode to cause the sheet processing apparatus to sandwich the sheet medium, on which an image has been formed by the image forming apparatus, between the two sheets of the two-ply sheet and cause the heat presser to laminate the two-ply sheet, and a second mode to cause the heat presser to laminate a sheet set that includes the sheet medium sandwiched between the two sheets of the two-ply sheet by a user.