An experimental investigation into the effect of corrosion on the ductility of steel reinforcement is reported. Both accelerated and simulated corrosion tests were conducted on bare bars and on bars embedded in concrete. The mechanism and degree of the reduction of ductility of reinforcement due to corrosion were examined. The influence of bar type and diameter on ductility of corroded reinforcement is discussed. The experimental results indicate that, since local attack penetration results in a significant variation of residual cross-section along its length, corrosion significantly reduces ductility of reinforcement. Although the strength ratio, elastic modulus and hardening strain only vary with bar type rather than corrosion level, the elongation, ultimate strain and ductile area of corroded reinforcement reduce much more significantly than do those of their yield and ultimate strengths. There is concern regarding bar ductility since about 10% corrosion may possibly decrease the ultimate strain of reinforcement below the minimum requirement specified in CEB Model Code 90 for class S reinforcement. Even though the elongation, ultimate strength and ductile area parameter of corroded small diameter andlor plain bars reduce more than those of large diameter and/or ribbed ones, such differences are not significant and can be neglected. Finally, a set of simple empirical equations is proposed to assess the ductility of corroded reinforcement in practice.