In this study, we attempted to clarify the electrical characteristics of diamond films synthesized by combustion flame and consequently synthesizing a suitable diamond film for use in electronic device applications. When the film contains amorphous carbon, the electrical resistivity (volume resistivity) decreases, i.e., the electrical characteristics of the diamond film worsen. To decrease the content of amorphous carbon in the diamond film, we utilized methods to detect two parameters: optimal equivalent ratio and optimal hydrogen addition rate. These methods can decrease the amount of amorphous carbon effectively, thereby systematically changing the factors influencing the optimal synthesis for improving the film's electrical characteristics. We have successfully developed a method for producing high-quality diamond films with excellent electrical characteristics and high electrical resistivity (10(10)-10(13) Omega m) at room temperature. This is a paper revealing, explaining and demonstrating the possibility of the controlled electric properties (DC) for diamond films synthesized by combustion flame. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.