Transparent conducting magnesium indium oxide films (Mgln(2)O(4)) were deposited on to quartz substrates without a buffer layer at an optimized deposition temperature of 450 degrees C to achieve high transmittance in the visible spectral range and electrical conductivity in the low temperature region. Magnesium ions are distributed over the tetrahedral and octahedral sites of the inverted spinel structure with preferential orientation along (3 1 1) Miller plane. The possible mechanism that promotes conductivity in this system is the charge transfer between the resident divalent (Mg(2+)) and trivalent (In(3+)) cations in addition to the available oxygen vacancies in the lattice. A room temperature electrical conductivity of 1.5 x 10(-5) S cm(-1) and an average transmittance >75% have been achieved. Hall measurements showed n-type conductivity with electron mobility value 0.95 x 10(-2) cm(2) V(-1) s(-1) and carrier concentration 2.7 x 10(19) cm(-3). Smoothness of the film surface observed through atomic force microscope measurements favors this material for gas sensing and opto-electronic device development. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.