The aim of this work is to study the effect of weathering grade on physical, mechanical and microstructure properties of metavolcanic aggregates and on mortars containing aggregates. Samples were collected from several locations in the Central and Southern Eastern desert in Egypt and they were characterised by XRF, polarized light, and SEM microscopy. Beside compressive strength, bulk density, apparent porosity and water absorption, modified weathering potential index (MWPI) was also determined based on the chemical composition of the rock aggregates. Seven mortars with metavolcanic aggregates were mixed and specimens were formed. Physical and mechanical properties of specimens were measured according to standards. Results showed that MWPI had the good relation with geotechnical properties of metavolcanic aggregates. Physical and mechanical properties of metavolcanic aggregates and concretes depended on weathering grade of rocks and on ratio of weathering minerals in aggregates.