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Al₂O₃-based ceramic cores were prepared by dry-pressing and subsequent pressureless sintering, where the Al₂O₃ powders were used as the matrix and the silicone resin powders were used as the binder. The effect of the silicone resin content on the properties of Al₂O₃-based ceramic cores was investigated. Results showed that the new mullite phase was formed by the reaction between Al₂O₃ and silica which was formed by the decomposition of silicone resin. Weight loss of sintered Al₂O₃-based ceramic cores was mainly caused owing to the release of gases during the cross-linking and decomposition process of silicone resin. And the release of gases inhibited the shrinkage caused by the sintering drive force. Therefore, with the increase of silicone resin content, more and more gases were released. As a result, the weight loss of Al₂O₃-based ceramic cores gradually increased and the shrinkage rate gradually decreased. The increasing silicone resin content made the apparent porosity increase and the bulk-density decrease, leading to the decrease of bending strength in sintered Al₂O₃-based ceramic cores. Although the addition of silicone resin decreased the bending strength, the dimensional precision was improved markedly.