In this work, we analyze the conductivity data of the nylon 6/FG nanocomposites using the normalized percolation equations and the general effective equation. From the interpretations of the derived results, we demonstrate that the microstructure of the nanocomposites can be readily deduced. Taking several factors into account, it turns out that the tunneling mechanism should be responsible for the observed non-universality of the critical exponents. Experimental evidences show that the existence of the tunneling conduction should be attributed to the particular structure of the prepared materials. (c) 2005 Elsevier Ltd. All rights reserved.