The present study characterized the kinetic, thermodynamic and performance parameters, products, factorial interactions, and optimal conditions of combustions of waste tea (WT) and tea leaves (TL) in N-2/O-2 and CO2/O-2 atmospheres through a thermogravimetric/Fourier transform infrared spectrometry (TG-FTIR). The main combustion occurred in the range of 200-600 degrees C. The increased heating rate increased all the combustion parameters regardless of the fuel and atmosphere type. Activation energy was shown different change tendency with the increasing conversion (alpha). CO2, H2O, CH4, CO, C=O, NH3, and HCN were the main gas products of WT and TL combustions. A three-way interaction among fuel type, atmosphere type and heating rate was found to be significant. The joint optimization of mass loss, derivative TG, and differential scanning calorimetry was achieved using 1049.3 degrees C, TL, 40 degrees C/min, and CO2/O-2 atmosphere for the operational settings of temperature, fuel type, heating rate, and atmosphere type, respectively.