The effect of zinc borate (ZnB) on the thermal and flame retardant properties of polyamide 6 (PA 6) composites containing aluminum hypophosphite (AlHP) was examined. The properties of the composites were investigated using thermogravimetric analysis (TGA), limiting oxygen index (LOI), horizontal burning test (UL-94 HB), vertical burning test (UL-94 V), and mass loss calorimeter (MLC) studies. According to the thermal test results, ZnB improved the thermal stability of the AlHP. Chemical interaction was observed between ZnB and AlHP. According to the flammability test results, the highest LOI value of 26.7 is observed with the addition of 5 wt% ZnB. However, UL-94 V rating turned to burn to clamp owing to the ceasing of dripping. All samples were classified as HB in UL-94 HB test. According to the MLC results, the lower peak heat release rate (pHRR) and total heat evolved (THE) were obtained with the addition of ZnB. Fire performance index (FPI) greatly improved with the use of ZnB. ZnB showed adjuvant effect in the condensed phase via increasing the residue yield with compact structure. (C) 2019 Elsevier Ltd. All rights reserved.