Abstract: The concentrations of dissolved inorganic manganese (DIMn), dissolved organic manganese (DOMn) in Sanggou bay were determined by the catalytic-kinetic spectrophotometry and UV digestion in April, July, October 2013 and January 2014.The contents of extractable manganese (HAc-Mn) and total manganese (TMn_s) in surface sediments were determined by two-step extraction in April, October 2013 and January 2014. The results showed that the average concentrations of DIMn in 2013−2014 were (62.0±43.4) nmol/L in April, (53.2±50.4) nmol/L in July, (20.5±7.4) nmol/L in October and (15.4±8.7) nmol/L in January and the average concentration of DOMn in 2013−2014 were (10.8±5.1) nmol/L, (14.5±18.3) nmol/L, (2.8±2.4) nmol/L and (7.5±3.7) nmol/L, respectively. The concentrations of DIMn and DOMn were higher in spring and summer than in autumn and winter, and gradually decreased from coastal to offshore. The average contents of TMn_s in surface sediment were (882±218) mg/kg in April 2013, (617±117) mg/kg in October 2013 and (625±64) mg/kg in January 2014 and the average contents of HAc-Mn were (508±151) mg/kg in April 2013, (335±83) mg/kg in October 2013 and (289±39) mg/kg in January 2014 respectively. The contents of TMn_s and HAc-Mn in the sediment were both decreased with the increasing distance from the coast, and the contents in spring and were higher than those in autumn and winter. The adsorption/desorption behavior on the suspended particulate matter and the utilization of plankton are important factors affecting the distribution and seasonal variation of dissolved manganese in the Sanggou Bay. The influcing factors of TDMn included the riverine and groundwater discharge, release from sediment-water interface and atmospheric deposition, the water exchange with the Yellow Sea and the absorption or accumulation by biological activities. Box model calculation results indicate that the total fluxes of different sources of TDMn in Sanggou bay are 41.9% lower than the sinks, indicating that there might exist other sources of TDMn in the Sanggou bay. The residence time of TDMn in the Sanggou bay is (44.9±41.1)d, which is significantly shorter than that in the ocean, and may be related to the special hydrological environment and the absorption and utilization of cultured organisms.