Pot experiments were used to study the effects of alginatederived oligosaccharide(ADO)synergistic urea on photosynthetic characteristics，key enzymes activities and carbon metabolites accumulation of rice(OryzaSativa L).The results showed that net photosynthetic rate(Pn)，stomatal conductance(Gs)，intercellular CO2 concentration(Ci)and water use efficiency(WUE)of rice under ADO synergistic urea treatment were increased，and stomatal limitation value(Ls)was decreased，compared with ordinary urea.Chlorophyll content and ribulose1,5bisphosphatecaboxylase(Rubisco)activity were also significantly raised.At booting，full heading and maturing stages，sucrose phosphate synthase(SPS)，sucrose synthase(SUS)and ADPglucose pyrophosphorylase(ADPase)activity in leaves or grain of rice were significantly enhanced，thus contributing to the accumulation of sucrose and starch in grain.Aboveground and belowground biomass were also significantly increased at all the four growth stages.Rice yield of ADO synergistic urea treatment was significantly raised by 9.32% compared with the control，and was higher than that of ordinary urea treatment by 3.94%.