Wood is a highly sustainable material for building construction, yet its susceptibility to fire hazards limits its structural applications. Nitrogen-phosphorus (NP)-based compounds are the most preferred fire-retardant (FR) additives for timber applications. But their use in wood also results in some negative effects, such as the loss of mechanical strength in wood. This study explores the synergistic effects of Nano-Silica (NS) and NP-based compounds on enhancing the fire retardancy and mechanical properties of Hevea brasiliensis. A combination of ammonium polyphosphate (APP) and dicyandiamide (DCD) has been used in this study as an NP-based entity. Wood samples were treated by the full cell impregnation process with the following compositions: a) NS only at 1.5% (w/w) concentration: NS_1.5; b) NP-based combination, APP (17%, w/w) and DCD (3%, w/w): APP₁₇/DCD₃; and c) combination of NS_1.5 and APP₁₇/DCD₃: NS_1.5/APP₁₇/DCD₃. During the rate of burning test, the control and NS_1.5-treated samples showed very poor fire resistance, reaching only 40% mass loss, almost within a minute, while APP₁₇/DCD₃- and NS_1.5/APP₁₇/DCD₃-treated samples reached the same amount of weight loss in 2.5 and 3 minutes, respectively. During the three-point bending test, the modulus of elasticity (MOE) showed 29% and the modulus of rupture (MOR) showed 43% deterioration in APP₁₇/DCD₃-treated samples as compared to the control samples. But the combined NS_1.5/APP₁₇/DCD₃ treatment recovered the deterioration in MOE and MOR values by making it almost equivalent to the control samples. Thus, the results of the experiments in this study confirmed the excellent synergy of NS and NP-based compounds in H. brasiliensis wood, not only enhancing fire resistance but also addressing the issue of mechanical deterioration in wood due to the NP-based FR treatment.