A lithological parameter dataset was created containing all geological descriptions of samples taken from the Belgian seabed. The information is a compilation of individual contributions of scientists associated to scientific institutes, national geological services and universities with a common interest in marine sediments. Descriptions were also extracted from geological reports of project-based sampling campaigns commissioned by authorities, enriched with confidential data from private companies and industry. Given the different origins of the data, as well as the timespan covered, harmonisation and standardisation were a necessity. To stimulate a coherent mapping throughout Europe, guidelines were established, e.g., EU-FP7 Geo-Seas for geological and geophysical data; EU-FP7 SeaDataNet for oceanographic data, INSPIRE for spatial information. To assure interoperability and compatibility of the data, lithological descriptions went through a coding procedure differentiating between main lithology, based on the Wentworth classification (1922); secondary lithology, based on Folk classification (1954); grain-size ranges with related mean and percentiles; sediment percentages (clay, silt, mud, sand, gravel and shell); as well as minor constituents like (in)organic and glauconite content. Colours were converted into indices. Metadata were quality-controlled and completed for nomenclature of boreholes, coordinates with geodetic reference datum and type of navigation system, data originator, services, ships or platforms, borehole age (or vintage), core depth, unique gear differentiation and interpretation method. The date and time of sampling were traced back from on-board documents and included in Coordinated Universal Time (UTC), a common international standard. Seabed depth was converted to meters below mean sea level (MSL), as it serves the need for a unified system between Belgium and the Netherlands. A (meta)data quality assessment for marine subsurface datasets has been worked out. A user-friendly digital data portal (www.bmdc.be/tiles-dataportal) holds for each borehole or sample (1) original documents with lithological descriptions and meta information; (2) lab results with grain-size data and information on the composition; (3) standardised and coded sheets from the originals with added data quality flags indicating the level of uncertainty on location, sampling gear and vintage; and (4) photographic material of cores and samples.