The use of biomass has been emerging as a worldwide trend. Although biomass is a renewable energy source, the disposal of generated by-products is an issue. A material with great potential for this purpose is oat husk. Nevertheless, no study has systematically investigated the influence of burning temperature on the characteristics of oat husk ash (OHA) and the use of this by-product as a supplementary cementitious material (SCM) and its influence on the properties in the fresh and hardened state of cementitious materials. The results showed that replacing up to 20 % of Portland cement with OHA burned at a temperature of 600 °C without compromising the cement pastes 7-d and 28-d compressive strength. The environmental analysis demonstrated the potential of oat husk as biomass and ∼ 24 % reductions in the eco-efficiency index of the composite matrices with 20 wt% OHA. Thus, this work identified the technical and environmental potential for the use of OHA as SCM for the production of sustainable cement-based materials.