Thermogravimetric and kinetic analysis of biomass and plastic co-pyrolysis can provide valuable inputs for a better understanding of decomposition mechanisms. Such inputs are important for selecting the appropriate process conditions but can also be helpful for process modelling. This work investigates the properties of heterogenous sawdust in a mixture with polypropylene and polystyrene. Thermogravimetric analysis is conducted to determine the decomposition mechanism and kinetic parameters of investigated mixtures and to derive appropriate conclusions regarding their further utilization potential. Co-pyrolysis was performed on mixtures with the following biomass/plastic ratios: 75-25%, 50-50%, 25-75%, over a temperature range of 30-550 °C, at four heating rates 5, 10, 20, and 30 °C/min, with pure argon as a carrier gas. Obtained results were then subjected to comprehensive kinetic and thermodynamic analysis. The primary goal was to determine effective activation energies using model-free methods, pre-exponential factors, and elementary thermodynamic parameters such as changes in enthalpy, entropy, and free Gibbs energy. Finally, the influence of the heating rate and mixture composition was extensively investigated by analyzing calculated parameters.