ASA emulsions costabilized by Laponite and polyaluminum sulfate (PAS) were prepared by homogenizing the mixture of ASA and aqueous dispersion of Laponite and PAS. The properties, sizing performance and hydrolysis resistance of the prepared ASA emulsions, were investigated in this article. The results show that the introduction of PAS significantly improves the stability, hydrolysis resistance, and sizing performance of ASA emulsions. The ASA emulsion stabilized by 0.5% of Laponite (based on total mass of emulsion) and 2% of PAS (based on the mass of Laponite) shows high hydrolysis stability and high sizing efficiency on bleached chemi-thermomechanical pulp. At the addition level of 0.3% based on bleached chemi-thermomechanical pulp, the sizing degree of ASA-sized paper can be as high as 120 s. Even when the storage time of the ASA emulsion exceeds 3 h, its sizing performance is hardly changed. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013