This investigation developed a systematic method to measure the temperatures and the mass concentrations of local species in a non-premixed ethylene-air flame using the holographic interferometry (HI) technique. A nearly linear state relationship between the Gladstone-Dale constant and the mixture fraction was deduced. Normalized state relationships between the refractive index and the mixture fraction were established from detailed combustion simulations for the NPFs. The maximum error of temperature caused by the assumption of composition of air was reduced from 48.84% to under 1.6% for the NPFs using the systematic method. The method can overcome the difficulty that the concentrations of local species must be known when measuring the temperature by HI for NPFs. (c) 2006 Elsevier Ltd. All rights reserved.