en Research Paper Research Paper Indium tin oxide (ITO) nanoparticles were synthesized by green combustion method using indium (In) and tin (Sn) as precursors, and <em>Carica papaya</em> seed extract as novel fuel. This paper highlights effect of tin concentration (5%, 10% and 50%) on microstructural, optical and electrical properties of ITO nanoparticles (NPs). The indium nitrate and tin nitrate solution along with the fuel were heated at 600 &deg;C for 1 h in muffle furnace and obtained powder was calcinated at 650 &deg;C for 3 h to produce ITO NPs. The above properties were investigated using XRD, FTIR, UV-Vis spectroscopy, SEM, TEM and computer controlled impedance analyser. The XRD, SEM and TEM investigations reveals the synthesized NPs were spherical in shape with an increase in average grain size (17.66 to 35 nm) as Sn concentration increases. FTIR investigations confirms the In-O bonding. The optical properties results revealed that the ITO NPs band gap decreased from 3.21 to 2.98 eV with increase in Sn concentration. The ac conductivity of ITO NPs was found to increase with increase in Sn concentration. These synthesised ITO NPs showed the excellent properties for emerging sensor and optical device application. Indium Tin Oxide,Green synthesis,Crystallite size,Band gap,Grain Boundary,AC conductivity 1 12 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-3811-2&slc_lang=en&sid=1 Mala Siddaramappa mala.s28@gmail.com 1800319475328460014747 1800319475328460014747 No Siddaganga Institute of Technology, Tumakuru, India Haraluru Kamala Eshwaraiah Latha lathahke@gmail.com 1800319475328460014748 1800319475328460014748 Yes Siddaganga Institute of Technology, Tumkur Haraluru Shankaraiah Lalithamba lalithambasit@yahoo.com 1800319475328460014749 1800319475328460014749 No Siddaganga Institute of Technology Andi Udayakumar udayk@yahoo.com 1800319475328460014750 1800319475328460014750 No Council of Scientific and Industrial Research-National Aerospace Laboratories