Dissolved stable silicon isotopes were determined in seawater samples collected during the 73rd expedition onboard RV Akademik Mstislav Keldysh (AMK73) in the Laptev Sea in October 2018 under ice free conditions. Seawater samples were filtered inline from Niskin bottles or the ship's underway system, acidified to 0.1% v/v with HCl and kept at 4°C until analysis on land. Samples were measured for δ29Si(OH)4 with reference to international reference material NBS28 on a Nu Plasma II MC-ICP-MS (The University of Edinburgh, School of Geosciences) using the MAGIC co-precipitation method and purified through column chemistry. International standards BigBatch, ALOHA300 and ALOHA1000 were run alongside seawater samples for inter-comparability. Final values were converted to δ30Si(OH)4 using the conversion factor of 1.96 for comparability. Reproducibility is 0.05 and 0.1‰ for δ29Si(OH)4 and δ30Si(OH)4 respectively. This dataset includes salinity, silicic acid concentrations and stable silicon isotope signatures of seawater, which provides useful information on the silicon biogeochemical cycle of the Laptev Sea, as influenced by the Lena river.