Selenite reacts with SeS3O 62− in acidic solutions forming selenanmonosulfandisulfonates with up to 6 Se-atoms in the chain. Se5S3O 62− and Se6S3O 62− have been detected for the first time. The decomposition causes precipitation of a sulfur/selenium-mixture. For the Se-precipitation giving reactions of SeO 32− with sulfite, S2O 32− , SeSO 32− , SeS2O 62− and SeS3O 62− a universal reaction scheme has been developed, prevailing of the following single steps: formation of monoselenandisulfonates, formation of build-up reagents, formation of higher selenopolythionates, decomposition of the selenopolythionates with the longest chains.