The in-plane cyclic response of reinforced concrete frames with unreinforced masonry infill was studied. Four full-scale reinforced concrete frame assemblies with masonry infills were designed and tested under reversed cyclic loading. The effect of panel aspect ratio and the stiffness of the infill relative to the frame were studied in terms of stiffness, strength, energy dissipation and failure mode. Based on the test results, an equivalent diagonal compression strut model was developed to represent the behavior of masonry infill bounded by a reinforced concrete frame and a simplified method for the linear-elastic analysis of R/C frames with masonry infills proposed. Using the experimental load-deformation plots, the hysteretic parameters relating to stiffness degradation, strength deterioration and pinching of the hysteretic loops were identified. These may be used to define the behavior of confined infills for the non-linear analysis of the infilled frames.