The impact of corrosion on the properties of steel reinforcement in concrete structures was examined. An experimental investigation was carried out in order to gain better insight of the effect of corrosion on the mass loss, fatigue and hardness, of BSt500s 12 and 8 mm diameter steel bars that were artificially corroded in a Sodium Chloride environment for different corrosion levels. The fatigue limit of the 12 mm steel was reduced by 20–40% and the mass loss was 1.5–2.9% for 15 and 30 days corrosion level, while the mass loss of the 8 mm steel was 1.2–32% for 10–90 days corrosion. The hardness of the 8 mm steel was reduced by 25–35% and 2–10% in the outer and inner layers of the specimens for 30 and 60 days corrosion respectively. Corrosion created considerable reduction in the fatigue strength and life of the steel bars due to drastic drop in the energy density, formation of pitting and notches along with destruction of the hardest outer layer of martensite.