Research in polymer nanofibers has undergone significant progress in the last decade. One of the main driving force for this progress is the increasing use of these polymer nanofibers for tissue engineering. Adequate porosity and surface area are widely recognized as important parameters in the design of scaffolds for tissue engineering and therefore measurement of porosity is very important. Previous methods such as mercury measurement, indirect method, the porosity measurement based on density of nanofibers do not measure the porosity of various surface layers. The goal of this study is measurement of porosity of various surface layers of scaffold. Image analysis was used for this purpose. SEM images of nanofibers mat were converted to binary images using different thresholds and porosity of scaffold was measured in various layers. On the basis of the results of our study, this method can be applied to porosity measurement of various surface layers of nanofibers mat. The results showed that porosity of various surface layers is related to the number of layers of nanofibers mat. (c) 2007 Wiley Periodicals.