On 2 April 2010, only one day after his resignation from Kavala, de Mos was named new manager of Sparta Rotterdam, replacing dismissed boss Frans Adelaar. He arrived at a time when the club was facing relegation with only a one-point advantage over 16th-placed ADO Den Haag. His adventure at Sparta started with little success: a 1–1 home draw to Heracles Almelo was followed by two consecutive losses, with his side being overtaken by ADO Den Haag, forcing the Rotterdam team to take part to the post-season promotion and relegation tournament in order to maintain its place in the Eredivisie.