The demand for fabricating ceramics with sophisticated shapes while exhibiting desired properties is increasing. Additive manufacturing (3D printing), enabling rapid prototype-less fabrication of complex-shaped ceramics, has attracted attention. Due to ceramics' low tolerance toward thermal shock, indirect selective laser sintering (SLS), which involves ceramic powder and a photocurable mixture is commonly used. Removing the photocurable resin during the debinding step often results in a porous structure, affecting the subsequent sintering process. This study investigates improving the sinterability of alumina ceramic paste for indirect SLS using composite particles. Composite particles were fabricated using the electrostatic assembly method, enabling homogeneous decoration of smaller additive alumina particles onto larger core particles. We also compared them with mixed powder obtained using different mechanical mixing methods. Our findings show that electrostatically assembled composite particles exhibit improved density and sinterability, which could be applied for additive manufacturing.