The effects of weight and stocking density on oxygen consumption and ammonia excretion of Trachinoms ovatus were determined by the closed flow experimental methods. The results showed that the oxygen consumption of juvenile T. ovatus decreased as its weight increased(P < 0. 05). Light had significant effects on oxygen consumption and ammonia excretion. The oxygen consumption and ammonia excretion of the fry under dark condition was 25. 18% - 40. 76% and 16. 28% - 40. 28% lower than these in the natural light conditions. The oxygen consumption of T. ovatus increased with the increase of stocking density. Ammonia excretion of T. ovatus showed the trend of hyperbola with stocking density increasing( P < 0. 05). Diurnal variation of oxygen consumption rate and ammonia excretion rate in T. ovatus was significant,average oxygen consumption and ammonia excretion in day time were higher than these at night,oxygen consumption in valley bottom value being 69. 68% of that of peak value and ammonia excretion in valley bottom value being only 30. 91% of that of peakvalue. The asphyxiation point of juvenile T. ovatus was 0. 991 ± 0. 058 mg /L.