Dataset comprises the results of a study into the engineering geological characteristics of tropical red clay soils, funded by the Overseas Development Administration. The geotechnical properties of a wide variety of red clay soils were determined by means of standard, specialised and new test procedures on both disturbed and undisturbed samples. These were obtained from selected study sites in a range of contrasting climatic, topographic and geological terrains, at various depths in weathering profiles. The majority of the study was undertaken in Kenya and Indonesia, in collaboration with local counterpart organisations (Ministry of Public Works, Materials Testing and Research Department, Nairobi; Institute of Road Engineering, Bandung). Study also included sample sites in Fiji and Dominica. The dataset includes detailed description sheets for the sampling sites, together with the laboratory programme of index and mechanical properties tests, much of which is held in digital format. All data from the study is available.