Flammability, fire performance, and thermal stability of short glass fiber reinforced polyamide-6 and polyamide-66 containing halogenated and halogen-free flame retardants (FRs) were compared. Flammabilities were assessed by limiting oxygen index tests and UL94 classifications. Fire behavior was evaluated by mass loss cone calorimetry, a bench-scale tool, to assess fire performance of materials. Halogen-free, phosphorus-based FRs were shown to perform superior to halogenated counterparts on the basis of important fire properties, peak heat release rate, time to ignition, and fire growth index. Moreover, thermal stabilities were maintained at an acceptable level as a clear advantage of halogen-free FRs.