Thermally synthesized polyaspartate (TPA, AmiSorb) is marketed as a crop growth enhancer. However, the stability and adsorption of this product in soils have not been fully evaluated. In this study, microbial degradation of TPA was determined in 10 different soils using14Clabeled TPA. Biodegradation, measured as mineralization (CO2production), varied with soil type ranging from 2.15% for a Hort Mix to 32.05% for the Pullman soil after 35 days incubation under the defined conditions. Percentages of degradation also varied with concentrations of the applied TPA. In most of the soils evaluated, TPA degradation rates were higher at 100 μg g−1than at 2 or 10 μg g−1after 35 days of incubation. In general, C and N supplements, as primary nutrients for microbial growth, reduced mineralization, suggesting that the level of readily available macronutrients in the soil influenced TPA utilization. Biodegradation of TPA was highly correlated with soil pH but was not correlated with any other soil parameters measured in this study, including Kd. The Kd values of the tested soils for TPA ranged from 10.6 to 98.8 mL g−1for the Norfolk and Bolfar soils, respectively.