This paper presents the effect of activator ratio and silica fume additive on physical and mechanical properties in slaked lime-based alkali-activated mortars which are limited in literature. The binder, which was formed by slaked lime and adding 5%, 10%, 15% silica fume into slaked lime, was activated with sodium hydroxide. The concentration of activator was chosen between 10 and 15 mol. The water/binder ratio was determined to be 0.55, and the binder/sand ratio was chosen as 1/3. After the produced mortar samples were placed in the mold, they were kept at 105 °C for 24 h at the activation temperature. The samples taken out of the oven were kept at room temperature (22 ± 2) ºC for up to 28 days. As a result of the experiments, in the samples containing 85% slaked lime and 15% silica fume, a compressive strength value of 36.46 MPa was determined. Compared with the control samples, it was observed that the flexural strength of the alkali-activated mortars produced with slaked lime increased by 3.72-fold and the compressive strength increased by 5.9-fold. As a result of the regression analysis, sodium hydroxide amount providing optimum flexural and compressive strength was determined as 14.28 mol, silica fume ratio as 10.03%.