The wildly-used charring agent, pentaerythritol (PER), was solely incorporated into polyamide 11 (PA 11) matrix by melt compounding. The addition of 15%PER improved the UL rating of PA 11-PER composites to V-0 and reduced the peak heat release rate by 22.1%. Most importantly, the time to ignition had been incredibly increased from 93 s of neat PA 11 to 193 s of PA 11-15PER sample. The thermal behaviors were investigated by thermogravimetric analysis (TGA) and TGA-Fourier transform infrared (FTIR). The morphology, chemical structure and physical properties (such as crystallinity and viscosity) of char residues that were collected at ignition point or after MLC tests of PA 11 and PA 11-15PER composites were fully demonstrated. It was suggested that the interactions between PA 11 and PER led to the rapid formation of a compact char layer which exhibited sufficient viscosity before ignition in the condensed phase, while the early released H2O and CO2 from PER took effects in the gas phase.