Polyvinyl Alcohol-Engineered Cementitious Composites (PVA-ECC) designed based on micromechanics exhibit high tensile ductility (above 1%) and limited crack widths (below 100 mu m). The tensile performance of ECC is dependent on the fiber and flaw size distributions. These parameters are known to be influenced by the matrix flowability and mix processing; however, a comprehensive quantitative analysis framework linking fiber and flaw size distributions to the tensile performance of PVA-ECC is needed to supplement theoretical understanding of the relationship between micromechanical parameters and composite macro-properties. In the present work, fiber distribution (dispersion and orientation) of two different ECCs in terms of matrix flowability was investigated using fluorescence microscopy and advanced digital image analysis. The maximum flaw size distribution along the specimens was also analyzed by cross-sectional image analysis. The influences of fiber and flaw size distributions on the composite behavior of PVA-ECCs were experimentally established. (C) 2013 Elsevier Ltd. All rights reserved.