Biodegradabilities of chelating agents were tested with activated sludge. Ethylenediaminetetraacetic acid (EDTA) remained intact in the effluent even after acclimation for 100 days, but propanediamine-N,N′-disuccinic acid (PDDS) and nitrilotriacetic acid (NTA) were biodegraded after acclimation for 5 and 23 days, respectively. Optical isomers of ethylenediamine-N,N′-disuccinic acid (EDDS) had different biodegradabilities:SS- andRS-isomers were susceptible to biodegradation, but theRR-isomerwas resistant.SS-isomer was degraded even by activated sludge without acclimation.