Abstract: Allelopathic rice “PI312777” and non-allelopathic rice “Lemont” were hydroponically cultured to explore photosynthetic physiological responses of different allelopathic rice accessions under low potassium supply. Morphological indices and photosynthetic physiological characteristics of two rice accessions respectively cultured in Hoagland solution at low potassium (5 mg·L^-1) and normal potassium (40 mg·L^-1) rates were investigated. The activities of three key enzymes associated with photosynthesis and expression of three key genes encoding enzymes were detected to evaluate the effect of low potassium on gene expression in two rice accessions. Results show that root length of “PI312777” is enhanced under low potassium supply and the revere is the case for “Lemont”. Plant height and dry weight are slightly inhibited in “PI312777”, but significantly drop in “Lemont”. Under low potassium supply, photosynthetic physiological characteristics indices such as net photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO₂ concentration, stomatal limitation and SPAD in “PI312777” slightly drop, but significantly drop in “Lemont”. Simultaneously, the activity and coding gene expression of ribulose 1,5-bisphosphate carboxylase, phosphoenolpyruvate carboxylase, and glycollic oxidase all decrease in two rice accessions under low potassium supply while significant decrease in non-allelopathic rice “Lemont”. The results indicate that “PI312777” has stronger photosynthetic ability and nutrition stress resistance.