Metastable ZrO2-x particles were successfully prepared by inert gas condensation (IGC) process. To control oxygen vacancies in metastable ZrO2-x, samples were annealed between 100degreesC and 400degreesC for 2 h under low oxygen partial pressures (PO2 = 10-15 Pa). Therefore, metastable ZrO2-x samples with various oxygen vacancies (0.26 < x < 0.81) were successfully fabricated by IGC method; also, the particle sizes were less than 10 nm.