In this study several parameters critical to the success of cryopreserving Sydney rock oyster (Saccostrea glomerata) larvae were investigated. They were: (1) cryoprotectants (10% dimethyl sulfoxide and 10% propylene glycol), (2) freezing protocols (with or without the seeding step), (3) larval concentrations (1,000, 3,000, 5,000, 10,000 and 30,000 individuals mL⁻¹), and (4) larval ages (6, 12, 24, 48, and 96 h old). The survival rates were determined as percentages of postthaw larvae performing active movements for the 6 and 12 h larvae or active cilia movement for the 24, 48, and 96 h larvae. Analyses showed that the difference in survival rates between different age classes was significant in all the experiments conducted, with the maximum survival rate being achieved in the 24-h-old larvae. When the freezing protocol without the seeding step was applied in 24-h-old larvae the postthaw survival rates of larvae cryopreserved with 10% dimethyl sulfoxide (93.1 ± 0.2%) were significantly higher (P < 0.001) than those with 10% propylene glycol (81.5 ± 0.4%). Differences in postthaw survival rates between different concentrations (1,000–30,000 individuals mL⁻¹) were not significant within each of the three larval age classes (6-, 12-, and 24-h-old) used.