KC-Al(OH)3/NR composites were prepared by adding a synergistic flame retardant system consisting of carrageenan (KC) precipitated by BaCl2 and nano-aluminium hydroxide (Al(OH) 3) to natural rubber (NR). The flame retardant was added into natural rubber (NR), and the flame retardancy and mechanical prop-erties of NR composites were tested by limited oxygen index (LOI), vertical burning test (UL-94), thermal gravimetric analysis (TG), cone calorimetry test (CCT). The NR containing 15 wt% KC and 15 wt% Al(OH) 3 displayed LOI value of 25% and UL-94 V-0 rating. CCT showed that the total heat release (THR), peak heat release rate (pHRR), peak smoke release rate (pSPR) and Average mass loss rate (AMLR) of NR de-creased by 65%, 12%, 23% and 62% when 15 wt% KC and 15 wt% Al(OH) 3 were added to pure NR.