In this study, indium tin-oxide nanoparticles (ITO-NPs), synthesized using in-situ reverse reduction (ISR2) method, were highly dispersed in an ink. ISR2 aims to reduce indium (In) and tin (Sn) ions dissolved in the HCI solution by putting it into the NH4OH solution with the dispersing agent included. In-Sn hydroxides were uniformly precipitated with a smaller size by applying the ISR(2 )method, and we confirmed ultrafine ITO-NPs of the sizes <10 nm after crystallization by heat-treatment at 400 degrees C. The ITO-NPs were well crystallized with cubic structure including (222) preferred orientation. BET specific surface area of the ITO-NPs was 95.47 m(2)/g, indicating that the average particle size was 8.75 nm. Balanced composition ratio of In to Sn (92.5 to 7.5 in weight) was made. In addition, the ITO-NPs were highly dispersed with a high zeta potential of 57.74 mV in absolute value when ink was formulated. Therefore, the ultrafine ITO-NPs were well made using the ISR2 method. Moreover, the ITO-NPs were successfully applied to the transparent heater for the extremely high temperature of 650 degrees C. Sheet resistance (R-s) of the ITO-NPs layer was 296.7 +/- 21.75 Omega/square when it was heat-treated at 1000 degrees C for 1 h, and it was lowered to 146.3 +/- 4.5 Omega/square by repeated heat generation at 150 degrees C. In addition, excellent heat-generating properties were confirmed by obtaining the extremely high temperature of 650 degrees C at 140 V. (C) 2018 Elsevier B.V. All rights reserved.