Citrus variegated chlorosis is a disease that attacks economically important citrus plantations and is caused by the plant-pathogenic bacterium Xylella fastidiosa. In this work, the structure of a small heat-shock protein from X. fastidiosa (XfsHSP17.9) is reported. The high-order structures of small heatshock proteins from other organisms are arranged in the forms of double-disc, hollow-sphere or spherical assemblies. Unexpectedly, the structure reported here reveals a high-order architecture forming a nearly square cavity.