A toner for a thermal transfer printing sheet is advantageous in terms of a fixing property to a release sheet, durability against deformation upon cooling, and a property of holding an image-forming toner, in addition to grindability and chargeability of the toner. The toner for a thermal transfer printing sheet is characterized by comprising a negative-charged crystalline polyester resin, wherein the toner has an average particle size D50 (volume) of 20 to 50 m.

The printing method includes an image forming step for performing a first process that forms an image on a transfer medium by ejecting a colored ink from a first inkjet head and an undercoat forming step for performing a second process including a process of overlaying undercoat ink on the image on the transfer medium by ejecting the undercoat ink from a second inkjet head, wherein assuming that a region where the adhesive is applied to the transfer medium at the same timing in the adhesive application step is a process unit region, in the undercoat forming step, the second process for the process unit region is delayed from an intermediate stage of the second process to completion of the second process.

The present disclosure is a thermal transfer sheet including a substrate and a transfer layer, the transfer layer containing a luster pigment, wherein, when an image of the sheet is taken from a side on which the transfer layer is present, the image is analyzed, dark and light portions of the analyzed image are inverted, automatic thresholding is performed in order to determine a threshold value of a brightness distribution, binary representation is subsequently performed, and the number and the total area of the black portions and the total area of the white portions are calculated, the ratio of the total area of the black portions to the total area of the white portions is 0.03 to 0.5, and the black portions have an average area of 100 to 300 m.sup.2.