We determined dissolved stable silicon isotopes along with silicic acid concentrations in geochemically well-characterized seawater samples recovered during the expeditions TRANSDRIFT-XX (TI12, March and April 2012), TRANSDRIFT-XXI (VB13, August and September 2013) and TRANSDRIFT-XXII (VB14, September and October 2014) to the Laptev Sea. During the winter TRANSDRIFT-XX expedition, samples were collected using 2-l-Niskin bottles mounted on a frame at several helicopter stations to the sea ice, while during the summer expeditions TRANSDRIFT-XXI and TRANSDRIFT-XXII the samples were recovered with a carousel water sampler equipped with 12 Niskin bottles (2.5 L) under ice-free conditions onboard the Russian research vessel RV Viktor Buynitskiy on the entire Laptev Sea shelf and above the shelf slope. The dataset includes dissolved stable silicon isotope and silicic acid concentration data, which provide important information on the distribution and biogeochemical cycling of silicon and other nutrients in the Laptev Sea.