Calcium-shellac microspheres with encapsulated carbamide peroxide (CP) were made by emulsification to generate an emulsion including shellac ammonium salt aqueous Solution with soluble CP dispersed in Sunflower oil with calcium chloride powders, followed by gelation between shellac and calcium. The effects of formulation and processing conditions on the encapsulation efficiency of CP, the physical, structural, and mechanical properties of calcium-shellac microspheres, including size, inner structure, and mechanical strength, were investigated. The sizes of the prepared microspheres were in the range of 10-100 mu m, depending on the agitation speed used in the emulsification process. The morphology of calcium-shellac microspheres was characterized using scanning electron microscopy and image analysis. Their inner structure was evaluated using X-ray microcomputed tomography, and their mechanical strength was determined by a micromanipulation technique. The Structure and mechanical strength of the microspheres were compared with those bigger calcium-shellac beads (1-3 mm in diameter) made by extrusion followed by gelation (Xue and Zhang, J Microencapsul 2008, 25, 523), and clear contrast in the properties between the two preparation methods has been found. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1619-1625, 2009