Flame retardant poly(butylene succinate) (PBS) composites were prepared by melt blending PBS with melamine phosphate (MP), using graphene or polyhedral oligomeric silsesquioxanes (POSS) as synergists. The comparative study on the effect of POSS and graphene on the mechanical, thermal properties and flammability of flame retardant PBS was investigated. The addition of POSS or graphene further improved the LOI values of the flame retardant PBS, and V) rating was obtained for the formulation containing 18 wt% MP and 2 wt% graphene. The incorporation of POSS and graphene reduced the crystallization of PBS, but improved the tensile strength. The presence of graphene exhibited superior thermal-oxidative resistance of the char layer compared to POSS, which effectively retarded the mass and heat transfer between the flame and the burning substrate, thus the heat release rate and total heat release of the flame retardant PBS composites containing graphene was significantly reduced during combustion. (C) 2012 Elsevier BM. All rights reserved.