Abstract: To explore the effects of instantaneous freeze-thaw cycles on the stabilization of aluminum in waterworks sludge, biochar from rice straw (RSBC), alkali modified attapulgite (AMAtp), and their combination (RSBC +AMAtp) were used to treat the aluminum sludge collected from a water treatment plant in southern Jiangsu. Following the stabilization, the treated sludge was subjected to 30 instantaneous freeze-thaw cycle simulations. Then, the morphology and structural features of the stabilization materials, the forms of aluminum and the basic physicochemical properties of the sludge after freeze-thaw cycles were analyzed. The results indicate that instantaneous freeze-thaw cycles promote the transformation of residual aluminum in sludge into extractable forms, such as acid-soluble inorganic aluminum. The content of extractable aluminum increases with the number of freeze-thaw cycles. After 30 instantaneous freeze-thaw cycles, the increment of extractable aluminum in RSBC, AMAtp and their combination decreased by 0.16%-12.13%, 23.63%-41.62% and 26.76%-56.05%, respectively, compared with CK. The pH of the three stabilization treatment waterworks sludge after instantaneous freeze-thaw cycles decreased by 0.23, 0.13, and 0.19 units respectively, whereas the EC decreased by 15.91%, 11.48%, and 14.43% respectively. The pH and EC were significantly negatively correlated with extractable aluminum (P < 0.01), indicating that instantaneous freeze-thaw cycles decreased the pH and EC of the drinking water sludge, subsequently facilitating the transition of aluminum from its residual form to an extractable form. Morphology and functional group characterization show that the instantaneous freeze-thaw cycle improved the functional group abundance of biochar from straw and the specific surface area of modified attapulgite. This enhancement leds to increased complexation and adsorption of extractable aluminum in waterworks sludge by both the materials, thus alleviating the influence of the instantaneous freeze-thaw cycle on the stabilization effect of the two stabilizing materials. Notably, the combined use of the two materials experienced the least influence from the instantaneous freeze-thaw cycles on their stabilization performance.