Porous Si₃N₄ ceramics were prepared by aqueous gelcasting using Si₃N₄ poly-hollow microspheres (PHMs) as pore-forming agent. The effects of solid loading of Si₃N₄ slurry and Si₃N₄ PHM content on the properties of porous Si₃N₄ ceramics were investigated. Only β-Si₃N₄ phase is observed in porous Si₃N₄ ceramics, and Si₃N₄ PHMs distribute uniformly both in Si₃N₄ green samples and porous Si₃N₄ ceramics. Results show that solid loading of Si₃N₄ slurry and Si₃N₄ PHM content could considerably influence the properties of porous Si₃N₄ ceramics. With the increase of solid loading of Si₃N₄ slurry (decrease of Si₃N₄ PHM content), the distributing state of Si₃N₄ PHMs changes from contacting with each other to just embedding in the matrix, thus their porosity decreases, while their shrinkage, flexural strength, and fracture toughness increase.