The previous experimental results on the circular steel tubes reinforced by a FRP composite have shown that the external reinforcement by composite improve their crush strength not only because of its own strength but also through an iteraction with the enveloped tube sheet which reduces the folding wave length and changes the collapse mode from an unstable one to a stable one. Here, the influence of the external reinforcement by composite on the crushing behaviour of square tubes is investigated experimentally. The same trend is obtained for square tubes. The external reinforcement changes the crushing mode from a non compact one to a compact one. The highest relative specific energy of the reinforced tube with respect to that of the non reinforced tube is 2.44.