This paper presents an analytical approach to predict the length effect on the postpeak ductility of concrete in compression. The approach takes into account the specimen length in calculating the ductility of concrete specimens under uniaxial compression and the influence of uniform moment zone length in determining the ductility of reinforced concrete beams. The uniaxial compressive response of concrete is considered using a strain localization-based approach that accounts for the size-dependent stress-strain response. The compressive response of the concrete is modeled by dividing the response into bulk and damaged sections. These different responses are used in the formulation of a systematic approach for predicting the size-dependent moment-top fiber strain response of reinforced beams in flexure. The decrease in postpeak ductility of longer reinforced concrete beams is captured by accounting for the effects of damage localization in the compression zone of the beam. The predicted structural response of variable-length, reinforced concrete beams was found to correlate reasonably well with experimental observations. Copyright © 2004, American Concrete Institute. All rights reserved.