This paper deals with the topic of using biomass ash in mortar production. There are already similar studies with the use of biomass ash in building materials as a substitute for a binder or an addition to the material. Some of these studies give positive results, thus claiming that ash improves the properties of the material. Also, there are studies with negative results which established that ash can be used only partially in exchange with other materials or that it cannot be used at all. These variations in research results from the fact that not all biomass ashes have the same properties. It is safe to say that the field of application of alternative materials in construction will continue to be a part of active research and study. Through this thesis, the very concept of biomass is treated, from which residues biomass is obtained and how it can later be used for useful purposes. Also, a significant part of the work reviews the eco-friendly aspect of the topic itself, given that the use of biomass ash is related to the reduction of pollution. The experimental part of the research investigates the possibility of using specific biomass ash as a partial substitute for cement and the influence of the substitute on properties of mortar in the fresh and hardened state. It is concluded that biomass ash has a bad effect on the workability of the mortar and its compressive strength, but there is a possibility of partial replacement of cement with biomass ash.