Two hypophosphites, aluminum hypophosphite (AlHP) and magnesium hypophosphite (MgHP), were applied to obtain flame retardant polyamide 6 (FR-PA6) composites. UL-94 and limiting oxygen index results indicated that AlHP contributed both good flame retardance and antidripping ability for PA6, while MgHP did not. Based on thermogravimetric analysis (TGA), AlHP and MgHP presented the different thermal degradation behavior. That is, the quick decomposition of AlHP took place at lower temperature than that of MgHP. AlHP promoted the early thermal degradation of PA6 and formed more char residue. The thermal decomposition mechanisms of AlHP and MgHP in nitrogen or air were suggested. Scanning electron microscope and X-ray photoelectron spectroscopy indicated that in the existence of AlHP, the morphological structures of char residue were more homogenous, and compact, and more char residue was formed. These results well illustrated the difference of the flame retardancy between AlHP and MgHP. Mechanical properties of PA6/AlHP and PA6/MgHP were also obtained. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012