To improve the alkali and heat resistances of Cl+Me-isothiazolinone (MCI/MI), a calcium alginate (CA) hydrogel sphere was used as the carrier for MCI/MI, and an MCI/MI/CA hydrogel sphere was prepared. Then, the release properties, alkali-resistance and heat-resistance properties, long-term antibacterial performance, and cytotoxicity of this novel hydrogel sphere were investigated. The results show that the CA hydrogel sphere released MCI/MI in a sustained manner with long-term antibacterial activity. Moreover, the CA hydrogel sphere improved the alkali and heat resistances of the MCI/MI. More importantly, this hydrogel sphere showed a slight cytotoxicity, which suggested that the MCI/MI/CA hydrogel sphere would be an easily added antibacterial hydrogel sphere for a wide range of products. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1554-1561, 2013