The 5AT/Sr(NO₃)₂ mixture has recently attracted attention as a gas-generating agent for use in novel fire-suppression applications. However, it cannot provide the desired combustion behavior alone. Thus, nitroguanidine (NQ) was added as a fuel component to 5AT/Sr(NO₃)₂ in attempt to improve the mixture's combustion behavior. The effects of NQ on the thermal and burning characteristics of 5AT/Sr(NO₃)₂ were investigated. Thermogravimetry-differential scanning calorimetric (TG-DSC) analysis with four heating rates (5, 10, 15, 20 K min⁻¹) under a nitrogen atmosphere was performed to determine the thermal characteristics and non-isothermal reaction kinetic parameters. The addition of NQ decreases the activation energy of the Stage II and III decomposition reaction, and accelerates the redox reaction and decomposition of Sr(NO₃)₂. Thermodynamic calculations and measurements of temperature profile and liner burning rates were performed to evaluate the combustion characteristics. Adding NQ decreased the adiabatic combustion temperature, outlet temperature, average flame height, flame oscillation frequency and pressure exponent of Vieille's equation, and increased the gas output and linear burning rate. Notably, mesa burning occurred when NQ was added, the mechanism of which is elaborated using a physical combustion model. The analysis deepens the understanding of when the gas-phase or condensed-phase reactions control the burning characteristics of the composite propellant.