In this study, the synergistic effects of natural pozzolan (NP) and limestone powder waste (LSPW) alkaline activated mortar has been investigated using compressive strength and microstructure analysis. LSPW was added in varying percentages to alkaline activated NP such that the combined ratio (LSPW/(LSPW + NP)) varied from (0 to 1) at the interval of 0.2. The activators used were sodium silicate (Na2SiO3(aq)) and sodium hydroxide (10M NaOH(aq)) combined as 1:1. The findings revealed that the synergistic effect of NP with LSPW emanated from silica and alumina required for the formation of aluminosilicate framework which required cation sourced from LSPW (Ca2+) for charge balancing in the formed skeletal framework. The products formed were mainly anorthite (CaAl2Si2O8) and gehlenite (CaO.Al2O3.SiO2). Besides, about 77 % of 28-days compressive strength (27 MPa) could be achieved in 24 h using heat curing. Microstructural analysis revealed that the rough texture of activated NP characterized with high porosity turned to be filled up by the presence of LSPW thereby improving the microstructural density.