To examine the effect of sustaining load at strengthening on the flexural behavior of strengthened reinforced concrete beams, six beams strengthened with carbon fiber-reinforced polymer (CFRP) laminates subjected to different sustaining loads are tested, in addition to two control beams without strengthening. The main experimental parameters include different levels of sustaining load at the time of strengthening, and reinforcement ratios. To explain the experimental results in quantitative terms, a theoretical model for flexural behavior of a strengthened reinforced concrete beam is also developed based on the displacement controlled nonlinear finite element method. Parametric studies for the strengthened reinforced concrete beam at different loading stages are performed using this model. Results of the experiments and model predictions showed that sustaining load levels at the time of strengthening have more influence on deflections of beams at yielding and at ultimate stage than on the ultimate strength of the beam.