A total of 202 lake sediment core records with ¹³⁷Cs data, representing 161 lakes from 119 publications (1980–2024), were compiled to build a database under the AVATAR Project ("A reVised dATing framework for quantifying geomorphological processes during the AnthRopocene"). The geographical focus was on the equatorial and Southern Hemisphere regions. The resulting ARLASH database (Artificial Radionuclides in LAke sediments of the Southern Hemisphere) is organized into several sections: general information, lake information, catchment information, ¹³⁷Cs data, ²¹⁰Pb data, sedimentation information, and publication details. A detailed description of the 55 extracted variables is available in the metadata sheet accompanying the ARLASH database.