Purpose Elevated concentrations of sulfate in groundwater are increasingly becoming a problem in several European cities. Building rubble from the World War II is assumed to be a major source of sulfate. This study characterizes pools of sulfur in rubble-composed technosols, and assesses their potential to release sulfate. Methods Six urban soil profiles have been analyzed. Fractions of the main technogenic components in the skeleton fractions were determined by hand sorting approximately 100 kg of material. Total sulfur and water-soluble sulfate were determined. Microplate-scale fluorometric assays were applied to measure the depth-dependent enzyme activity of arylsulfatase. The mineral composition of soil samples was analyzed using powder X-ray diffractometry. Binding forms of sulfur were determined using X-ray absorption near-edge structure spectroscopy. Results The maximum total content of sulfur is 4.6 g·kg −1 ; that of readily soluble sulfur is 2.3 g·kg −1 . Both gypsum and traces of barite and ettringite were detected in some fine soil and component samples. Samples taken from deeper