Supplementary cementing materials (SCM) have become an integrals part of high strength as well as high performance concrete mix design. These materials are used extensively throughout the world for their good performance and for ecological and economic reason. However, environmental concerns both in terms of damage caused by the extraction of raw materials and CO2 emission during cement manufacturing have brought about pressure to reduce cement consumption by the use of (SCM). The most common cementitious materials that are used as concrete constituents, in addition to Portland cement, are fly ash (FA), ground granulated blast furnace slag (GGBS), silica fume (SF), rice husk ash (RHA) as well as Metakaolin (MK). This paper presents the results of an experimental study undertaken to investigate the performance of Portland cement based mortar mixes incorporating combinations of nano-metakaolin particles (NMK) as well as (FA) and (SF) as partial replacement of cement under elevated temperature. 5%, 10%, 15% and 20 % total pozzolanic materials used as a partial replacement of cement beside the control mix. The degradation of the compressive strength was investigated after being exposed to elevated temperature levels of 200, 400, 600 and 800 C° and the results were evaluated compared to those at ambient temperature of 27 C°. The results of this investigation indicate an improvement of the performance of Portland cement based mortar mixes containing different quantities of pozzolanic materials as partial replacement of Portland cement when subjected to elevated temperatures. Moreover, the best performance evaluated based on loss in compressive strength was noticed for mixes containing combination of NMK and FA that introduces such materials as a fire resistance building materials.