A justifiable replacement for pozzolana that utilizes industrial wastes is needed due to the growing concern on CO₂ emissions associated with cement. The effect of heat treatment of pumice powder (PP) on mechanical and durability properties of cement mortar was investigated in this study. Nine different mixes of mortars with varying cement replacement levels (10 %, 20 %, 30 %, and 40 %) by weight of PP were prepared. The PP was treated at 100 ℃ (P-100) and 700 ℃ (P-700). Strength activity index (SAI), water demand, setting time, and flow characteristics were determined. Mechanical properties and porosities were also measured and determined at the age of 7, 28, 56, and 90 days. Moreover, mortar samples were exposed to acidic media for 120 days to assess durability. Results of the SAI showed that the high pozzolanic potential of P-700 is attributed to amorphous silica (SiO₂) and detected in the X-ray diffraction test. The PP content showed a positive effect on setting times and flowability of mortars. Moreover, 20 % replacement at all ages achieved maximum mechanical properties while 30 % replacement at later ages improved the mechanical properties compared with the control mix. Notably, high replacement levels of PP enhanced the resistance against acidic attack. The SEM-EDX analysis along with Thermogravimetric Analysis (TGA) test verified the better performance of P-700 over P-100.