Abstract: In July, 2012, a measurement was made on the oxygen consumption rate and ammonia excretion rate of three body sizes of Bullacta exarata in the Laizhou Bay of East China under effects of salinity 18, 23, 28, 33, and 38. The results showed that salinity, body size, and their interaction had significant effects on the oxygen consumption rate (OR) and ammonia excretion rate (NR) (P<0.05). Within the range of the salinity 18-28, the OR and NR increased with salinity, and peaked at salinity 28. With the further increase of the salinity, both the OR and NR decreased. The relationships between the OR and NR and the dry weight of soft-tissue could be expressed as exponential equation. The O/N mole ratio varied from 8.38 to 29.16, and reached the maximum at salinity 33. According to the calculation of individual  biomass and ammonia excretion rate, the ammonia production from the B. exarata in the Bay was estimated as about  66.53 mg N·hm^-2·d^-1,  which could affect the organisms of the same ecological niche and the N-cycle in the Laizhou Bay.