The study focused on finding the cheapest construction material besides creating awareness for society to use available construction materials, it also focused on saving virgin materials. . Therefore, this research studied sawdust ash as a supplementary cementing material using mortar with various tests in the fresh, hardened, and microstructure of cement mortar. The partial replacement of cement with 5%, 10%, 15%, 20%, 25%, 30%, 35%, and 40 % of sawdust ash was executed with 0.55 water-cement ratio and 5%, 10%, 15%, and 20% of saw-dust ash was executed with 0.485 water-cement ratio at 3 rd days, 7 th days, 28 th days, 56 th days and 91 st days curing ages in contrast to the reference (control mix). To meet the objectives, the study: X-ray fluorescence (XRF) was implemented for the sawdust ash; consistency, soundness, setting time and flow table were implemented for the fresh cement mortar (cement paste); compressive strength, ultrasonic pulse velocity, sulphate attack, and water absorption were implemented for harden cement mortar; Fourier transform infrared spectroscopy was implemented for microstructure of mortar cubes; and finally, BET was implemented for physical properties of cement mortar. The results show that sawdust ash saw dust ash of Cordia Africana (Wanza), Eucalyptus camaldulensis (Bahir-Zaf) and Juniperus procera (Tsed) is a cementatious material with chemical composition (SiO2 + Al2O3 + Fe2O3) 28.62% of of SDA and 31.22% of CaO. The fresh properties of sawdust ash blended mortar affected by the saw dust ash percent in the mix increases; however, 5% of SDA replacement does not show any significance variation with the control mix. The partial replacement of cement with SDA in the harden mortar cubes shows an improvement at 5% replacement, though others show the decreasing in compressive strength, UPV, sulfate attack resistance, and increasing of w ater absorption than the reference mix. This research takes the attention of the stakeholders in the construction sector. Because the majority of the people of Ethiopia use wood products for cooking and other domestic purposes while the ash is practically a waste that is found abundantly. Therefore, using the sawdust ash as partial replacement cement in the production of cement mortar positively affects the growing construction industry in the country. Keywords: SDA, Cement Mortar, Compressive Strength, UPV, Sulphate Attack, Water Absorption, Microstructure, Water-Cement Ratio