The pH-sensitive poly(vinyl alcohol)/poly (acrylic acid) hydrogel microcapsules containing vitamin B-12-loaded Al2O3 core were prepared with a three-step emulsion polymerization. Al2O3 was chemically treated with HCl or NaOH solutions at room temperature for 24 h to modify the binding properties with vitamin B-12. The colon-targeted release characteristics of vitamin B-12 from the microcapsules were evaluated at different pHs. These microcapsules showed the faster and larger release of vitamin B-12 due to the high swelling of microcapsule shell as the pH was changed into more basic condition. However, these microcapsules showed the slower and less release of vitamin B-12 as the acid value of Al2O3 increased due to the strong binding interaction between Al2O3 core and vitamin B-12 even though the initial loading of vitamin B-12 was higher. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1853-1858, 2010