The interfacial interaction of flame retarded and glass fiber reinforced PA66 composites is a very important issue due to one of the key factors influencing the mechanical properties of materials. In this article, the interfacial interaction among the components in the composites has been Studied by IGC/DSC/SEM techniques. The experimental data demonstrated that Zn2+-modified melarnine polyphosphate (Zn-MpolyP) flame retardant could obviously enhanced the mechanical properties of the composites compared with melamine polyphosphate (MpolyP). SEM results proved that Zn-MpolyP could well disperse in the composites, and effectively improve the interfacial compatibility of the composites. Based on DSC results, Zn-MpolyP and MpolyP promoted the crystallization enthalpy (Delta Hc) and temperature (T-c) of PA66 to increase. Zn-MpolyP showed more effect in increasing the crystallization degree of PA66 than MpolyP. They exhibited the nucleating effect in PA66. The Lewis acid-base numbers (K-a and K-b) and their ratio (K-b/K-a) obtained by inverse gas chromatography (IGC) further proved that the strongest Lewis acid-base interaction between PA66 and Zn-MpolyP existed in the composites. This result is probably due to the strong complex between Z(2+) in Zn-MpolyP and lone pair electrons at O and N atoms of PA66 and glass fiber. Therefore, the all results of IGC/DSC/SEM techniques dernonstrated that the interfacial compatibility of components in composites was better improved by Zn-MpolyP than MpolyP. (C) 2008 Elsevier Ltd. All rights reserved.