In this paper, in-situ coagulation of 0.9Al₂O₃–0.1TiO₂ suspension and microwave dielectric properties of 0.9Al₂O₃–0.1TiO₂ ceramics prepared by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method were proposed. The 0.9Al₂O₃–0.1TiO₂ suspension could be coagulated via controlled release of calcium ions from calcium iodate at an elevated temperature. The influence of tri-ammonium citrate (TAC) content, solid loading, and calcium iodate content on the rheological properties of the suspension was investigated. In addition, the influence of coagulation temperature on coagulation time and properties of green bodies was also studied. It was found that the stable 0.9Al₂O₃–0.1TiO₂ suspension could be successfully prepared by adding 0.3 wt% TAC and adjusting pH value to 10–12 at room temperature. 0.9Al₂O₃–0.1TiO₂ green bodies with uniform microstructures were coagulated by adding 8.0 g/L calcium iodate after treating at 70 ℃ for 1 h. 0.9Al₂O₃–0.1TiO₂ ceramics, sintered at 1500 ℃ for 4 h and annealed at 1100 ℃ for 5 h, showed uniform microstructures with density of 3.62±0.02 g/cm³. The microwave dielectric properties of 0.9Al₂O₃–0.1TiO₂ ceramics prepared by DCC-HVCI method were: ${\epsilon }_{\text{r}}$= 11.26±0.06, Q×f = 11569± 629 GHz, ${\tau }_f$= 0.93±0.60 ppm/℃. The DCC-HVCI method is a novel and promising route without binder removal process to prepare complex-shaped microwave dielectric ceramics with uniform microstructures and good microwave dielectric properties.