Current models of the elasto-plastic behaviour of unsaturated soils contain important underlying assumptions that have not been tested due to a lack of adequate experimental data. To address this issue, the objective of this paper is to provide a comprehensive set of experimental data An extensive experimental program has been performed on a remoulded unsaturated silt. To characterise its elasto-plastic behaviour, samples were taken through various stress paths, including wetting, drying and compression. Experimental results were analysed to provide (1) evidence of suction-induced preconsolidation; (2) dependence of cohesion and shear strength at failure on suction; (3) stiffness in relation to suction and (4) uniqueness of the critical state line.