To prevent disaster in future earthquakes, one way of retrofitting the members in reinforced concrete buildings is concrete jacketing. The present study investigated the effect of jacketing on the flexural strength and performance of beams. First, slant shear tests were conducted to study the interface between old and new concrete. Second, beam specimens were tested to study the effect of jacketing on the positive bending of the span region. Third, beam-column-joint sub-assemblage specimens were tested to study the effect of jacketing on the positive bending of the beams adjacent to the joint. Analytical investigations were carried out to predict the experimental results. A layered approach was used for the prediction of the moment versus rotation curves for the retrofitted beam specimens. An incremental nonlinear analysis was adopted to predict the lateral load versus displacement behaviour for a retrofitted sub-assemblage specimen. Guidelines for retrofitting of beams by concrete jacketing are provided.