Agricultural and industrial by-products are commonly used in concrete production as cement replacement materials (CRMs) or as admixtures to enhance both fresh and hardened properties of concrete as well as to save the environment from the negative effects caused by their disposal. This paper presents some findings on the effect of Microwave Incinerated Rice Husk Ash (MIRHA) on workability and compressive strength of concrete. It was obtained that the inclusion of MIRHA as partial replacement of cement could significantly improve the compressive strength of hardened concrete while reducing the workability of fresh concrete. © (2014) Trans Tech Publications, Switzerland.