The technique of strengthening concrete structures by epoxy bonding the steel plates to the tension face of the structure has been widely used in civil engineering. In this paper, the surface preparation of the concrete and steel plates is described and then the bonding technique is discussed. The influence of the adhesive thickness and the steel plate thickness on the behaviour of strengthened concrete beam is investigated. Beams with six different thicknesses of adhesive layer and five different thicknesses of steel plate were used in this study. The measured load versus strain curves for both the steel plate and the concrete of the strengthened beam were plotted. The results indicate that the ultimate flexural strength does not increase with increasing thickness of the adhesive. The strain at the first cracks in the concrete is unchanged with increasing adhesive thickness. However, at higher loads, the strain in the plate, as well as in the concrete, increased with increasing adhesive thickness. The strain in the steel plate increased at the same rate as that in the concrete in the elastic region and then the strain in the steel plate increased at a much faster rate for the same beam. The results also indicate that the strain corresponding to the ultimate load in the steel plate decreased with increasing plate thickness. The stiffness of the beam increased with the plate thickness, especially in the higher load range.