This paper presents a transient thermal analysis of a rocket nozzle employing Fluid-Structure Interaction (FSI) simulations. In case of solid fuel, the nozzles are not cooled by the liquid propellants. Consequently, the temperatures on the nozzle wall are high which demands the usage of special materials for the nozzle to withstand thermal loads and protect surrounding structures. The application of different materials and the intricate geometrical interfaces between them may led to high stresses and thus to component failure. The presented analysis will determine the transient heating process of the structures, the resulting thermal loads and the generated stresses. Thermal and flow properties in the hot gases are simulated using computational fluid dynamics (CFD) while the thermal field in the structure is obtained employing finite element analysis (FEA). Based on the nature of the flow in the nozzle, an assumption to simplify the complete FSI procedure is presented. The steady state flow in the nozzle is not significantly changed due to the changing temperatures on the nozzle wall. Therefore, the CFD part of the FSI simulation is considered as steady state while the FEM structural thermal analysis is still transient. Similar approach is presented in [1], where only a small portion of structure, namely only ‘thermal protective layer’, is observed and analysed with a conjugate heat transfer approach. By analysing the thermal and structural responses of the rocket nozzle, the simulation results allow for critical insights on heat distribution patterns, temperature gradients, and potential failure modes. The presented approach is firstly validated on the test nozzle. At the end the simulation result of the real geometry is compared to the test results of the real geometry.