Predictingthethermalperformanceofcomplexaerospacestructuresrequiresaccurateknowledgeofthethermal properties associated with the structure. It is desired, in this case, to measure the in situ properties of a complex as-built structure, not only to capture the thermal properties of each component but also to capture interaction of components in the as-built structure. The overall goal of this study was, therefore, to develop and implement a nondestructive methodology to estimate the thermal properties associated with a complex aerospace structure. The structure considered was an outer wing subcomponent design for the high-speed civil transport made from four different materials, including a honeycomb blanket. The thermal properties sought included both effective and individual material through-the-thickness thermal conductivities and volumetric heat capacities (product of density and specie c heat ) and the in-plane thermal conductivities of each material in the structure. In the estimation procedureanobjectivefunctioncontaining boththeoreticalandexperimentaltemperaturehistorieswas minimizedusing ageneticalgorithm.One-dimensionalexperimentswereimplemented toestimatethethrough-thethicknessthermalconductivitiesand volumetricheatcapacities, andtwo-dimensionalexperimentswereconducted to estimate the in-plane conductivities. These properties were successfully estimated despite the high degree of correlation and low sensitivity evident for many of the properties.