Cigarette butts (CB) rank at the top of littered waste materials and can cause a serious impact on the environment. CB are mainly composed of cellulose acetate (CA) fibers, a polymer that has poor biodegradability. Following the growing concern to reduce pollution, this study presents an innovative way to recycle industrial treated CA fibers by incorporating them in cementitious mortars as partial replacement of sand. CA fibers are found to be porous, with a total porosity of 97%, to have a bulk density of 65 ± 2 kg/m3 when compacted and to have a high water absorption of about 853 wt% that is higher than other bio-sourced materials. Optimal formulations based on workability tests are 0.2 wt% of sand replacement by CA without the use of a superplasticizer (SP), and 1.3 wt% with 3 wt% of SP. The compressive and bending strengths, and the total shrinkage of the reference mortar are close to those the of the 0.2 wt% CA contained mortars, as they have close porosity. The latter increases for 1.3 wt% CA (and SP) contained mortar leading to a decrease in mechanical strength and an in increase in shrinkage. Thermogravimetric analyses (TGA) reveal that the quantity of water released by the CA fibers enhances the cement hydration.