A systematic investigation on the microstructural assay of aromatic polyamide membrane material has been presented. The study constitutes important aspects like critical micro-void size determination and the relative concentration of the same in the different samples synthesized using positron annihilation lifetime spectroscopy (PALS). Furthermore, assay of the partial crystallinity with the wide angle powder diffraction method and electron diffraction pattern along with the transmission electron micrograph (TEM) yields the micro-morphological description of the membrane material under investigation. The effect of ionizing radiation (Co-60 gamma-rays, similar to110 kGy) on the membrane material is found to have a significant increase in the relative population of the voids as examined through PALS. An FTIR spectroscopic analysis before and after irradiation of the sample is also presented. These a priori informations are expected to be useful in determining the efficacy of the desalination performance of this polyamide membrane material. (C) 2003 Elsevier B.V. All rights reserved.