One of the main problem in resin transfer molding (RTM) is the formation of microvoids decreasing the mechanical performance of the components. In this study, an ultrasonic inspection method (C-scan) was used to evaluate these microvoids. Composite sample plates were produced by a small laboratory size RTM machine injecting epoxy resin into a flat mold filled with woven carbon fiber layers. In C-scan analysis a certain value of energy loss (dB loss) was selected as the 'operator set level' and further dB losses were considered as 'defect' or 'microvoid'. C-scan inspection indicated that increasing injection pressure above 2 atm increases the number of microvoids leading to decreased mechanical properties. In the second part of this study, optical and electron microscopy were used to examine these microvoids and also failure mechanisms of the samples. (C) 2004 Elsevier Ltd. All rights reserved.