ZrO2 microspheres were prepared with an improved internal gelation process without cooling the precursor solution. The stability of the broth for internal gelation process has been systematically investigated, and the results show that the preparation and storage temperature, the concentration of NO3- and the urea in the broth have important effects on the stability of the broth. Through optimizing the broth formulation the broth prepared can be stable for 14h at 25 degrees C. The prepared ZrO2 ceramic microspheres have uniform size and good sphericity, with a density of 5.87g/cm(3).