The effect of high temperature treatment of ordered mesoporous carbons (OMCs) under neutral atmosphere is studied for OMCs prepared by using different carbon precursors (furfuryl alcohol, sucrose, acenaphthene and mesophase pitch) and different ordered mesoporous silica (OMS) templates (MCM-48 and KIT-6). The OMS-templated carbons were thermally treated at various temperatures ranging from 900 °C to 2400 °C to study changes in their porosity and framework crystallinity. The KIT-6 silica was synthesized at different conditions to control the size of primary mesopores and interconnecting complementary pores. The use of MCM-48 silica as template afforded the carbon replicas, CMK-1, which underwent a structure transition from Iad to I41/a. The use of the KIT-6 silica template, depending on the size of complementary pores, afforded a faithful inverse replica, CMK-8, as well as the CMK-1-type structure that underwent the aforementioned symmetry transition. The XRD patterns for the carbons studied showed that their thermal treatment led to a gradual deterioration of the carbon structure, which was associated with structure shrinking and pore walls fracturing. Particularly significant changes in the structural properties of the carbons studied occurred for those heated (graphitized) at 2400 °C, which manifested itself in a partial or complete loss of the pore volume. It was found that the CMK-1-type graphitized carbons exhibited better thermal stability, which is reflected by the presence of residual mesopores and/or nanostructure ordering. The degree of graphitization for the carbons heated at 2400 °C depended insignificantly on the type of carbon precursor; however, the precursor effect became more pronounced with decreasing temperature of the thermal treatment.