For stereolithography (SLA) 3D printing applications, Al2O3 ceramic particles with a different coating thickness of silane coupling agent (VTES, vinyltriethoxysilane) were prepared by hydrolysis and condensation reactions. Then, VTES-coated Al2O3 ceramic particles were dispersed in commercial photopolymers (3DK-A83B) based on inter-penetrating network (IPN) phenomena. The morphology and average coating thickness of VTES-coated Al2O3 ceramic particles were observed by field-emission transmission electron microscopy (FE-TEM), and the particle size of VTES-coated Al2O3 ceramic particles was investigated by a laser scattering particle size distribution analyzer. The dispersion stability of the VTES-coated Al2O3/3DK-A83B composite solution with different VTES coating thicknesses and ceramic contents was investigated by Turbiscan and relaxation nuclear magnetic resonance (NMR), while the optimum coating conditions for VTES were also observed. In the case of Al2O3 ceramic particles with a similar VTES coating thickness, the dispersion stability was similar, even when the ceramic content increased. The cross-sectional images of 3D-printed objects were observed by field-emission scanning electron microscopy (FE-SEM), and about 48% of volume shrinkage of the 3D-printed objects was calculated after sintering.