The SeaDataCloud Temperature and Salinity Historical Data Collection for the Baltic Sea include open access in situ data on temperature and salinity for the period 1900 – 2019. The data were retrieved from the SeaDataNet infrastructure at the end of August 2019. The dataset format is ODV binary collections. The quality control of the data has been performed with the help of ODV software. Data Quality Flags have been revised following common recommended procedures defined under SeaDataNet 2 project in conjunction with visual expert check.