Weight of individual grains is a major yield component in wheat. The non-uniform distribution of single grain weight on a wheat spike is assumed to beelosely associatted with starch synthesis in grains. The preseint study was undertaken to determine if the enzymes involved in starch synthesis caused the difference in single grain weight between superior and inferior grains on a wheat spike. Using two high-yield winter wheat (Tritieum aestivum L.) varieties diffeing in grain weight and theree nitrogen rates for one varity, the contents of amylse and amylopection, and activities of enzymes involved in starch synthesis in both superior and inferior grains were investigated during the entire periol of grain filling. Superior grains showed generally higher starch accumulation tates and actieties of enzymes ineluding SS (sucrose synthaes), UDPGP Pase (UDP-glucose pyrophosphorylase), ADPGPPase (ADP-gluceose pyrophosphorylase), SSS (soluble starch synthase) and GBSS (starch granule bound starch synthase) and subsequently produced much higher single grain weigth than inferior grains. Nitrogen inereased enzyme activities and starch accumulation rates.and thus improved individual grain weight, especially for inferior grains. The SS. ADPGPPase and SSS were significantly correlated to amylopectin accumulation, while SS, ADPGPPase, SSS and GBSS were signinficantly correlated to amylose accumulation. This infers that SS, ADPGPPase and starchsynthase play key roles in regulating starch accumulaition and grain weight in superior and inferior grains on a wheat spike.