This paper presents a collection of data obtained at different locations concerning Miocene clays, which form a significant part of Lisbon subsoil. The data includes both laboratory and in situ tests, namely: mineralogical characterization; determination of index properties; grain size distribution; natural water content and Atterberg limits; uniaxial compression tests; triaxial compression tests; SPT and cross-hole seismic tests. The characterization of a particular site concerning Miocene clays and including both laboratory and in situ tests is presented. The amount of information is very significant allowing for the establishment of some basic trends on the geotechnical characteristics of these soils.