Ozonation of seawater produces residual oxidants which do not occur in fresh water. Most of them are bromine compounds, such as HBrO. In this study, the acute toxicity of these ozone-produced oxidants (OPO) to eggs and larvae of Japanese whiting, Sillago japonica, was tested under static-flow conditions of water with a temperature of 21.6 ?? 23.1°C, salinity 33.4 ?? 34.4‰, and pH 8.2 ?? 8.3. In analysis of the results, initial OPO concentrations measured as total residual chlorine were given importance since OPO disappeared gradually through contact with eggs or larvae. Based on the initial OPO concentration and normal survival rate, LC₅₀'s were estimated as 0.18mgC1/l (after 38h) and 0.23mgC1/l (after 24h) for eggs and larvae, respectively. Eggs were found to delay hatching. Many eggs exposed to near sublethal OPO stayed unhatched beyond the expected hatching time. After that, the death of these eggs was observed.