In this study, the capacity, rupture and ductility of circular reinforced concrete columns reinforced with glass-fibre reinforced plastic pipes and carbon-fibres reinforced plastic, under eccentric load was checked. The effects of eccentricity, casing, twist and number of layers on the behaviour of the columns were evaluated. Eighteen circular columns with and without casings, with diameters and heights of 150 and 600 mm, respectively, were subjected to axial loads with eccentricity of 20 and 50 mm, and the effects of GRP and CFRP as the enclosing factors of the columns were investigated. The results showed that the use of casing and twist separately and simultaneously causes a significant increase in the compressive capacity of the columns. On average, the addition of one layer and two twisted layers with and without casing, increased their capacity by 24%, 34%, 6. 3% and 12%, respectively. The number of twisting layers did not have much effect on the ultimate compressive capacity in the columns with casing,while the casing increased the compressive capacity of the columns by 3. 5 times on average. Rupture occurred in columns without casing mostly locally and gradually, and in columns with casings completely,the cause can be attributed to the very high degree of enclosure caused by the casing. The use of casing increased the ductility of reinforced concrete columns by a large amount, so that the average increase in axial displacement in columns with casing compared to similar columns without casing, was 399%.