Reinforcement steel rebar is produced by several ways but most importantly the tempcore process. Due to mass production in steel rolling plants, the rebars are gathered after tempcore process at a specific temperature in bundles stack in the warehouse. The bundling temperature varies from 200 to 300 o C. The rebars need relatively long time, up to one day, to reach the room temperature in the bundles stack. This work investigates the effect of prolonged ageing time on the rebars mechanical properties after the tempcore process of both ageing in bundle and designed artificial ageing. The results of mechanical properties of ageing in bundle compared to the artificial ageing were found to be in good agreement. The yield and tensile strengths were found to decrease by 6.3 and 2.1 %, respectively, due to artificial ageing. However, the elongation and the tensile to yield ratio increased by 17.6 and 4.8 % respectively.Ageing process Tempcore process Reinforcing steel rebar Microstructure Mechanical properties