Abstract: To study the effect of GA3 on yield and nutritional quality of Amaranthus tricolor and its residue dynamic, and provide a scientific basis for establishment of technical regulations for safe and effective use of GA3 in edible amaranth cultivation, GA3 was applied at high, middle and low levels (90, 60 and 30 g/hm2) when the edible amaranth had 5-6 leaves in summer of Guangzhou. The height, yield, vitamin C, protein, reducing sugar, soluble solids and crude fiber of edible amaranth in different stages were investigated. Effect of GA3 in different dosages on height, yield and nutritional quality of edible amaranth was discussed. Terminal residues and dissipation dynamic of GA3 were also evaluated. The height and yield of edible amaranth rose significantly under the middle dosage level of GA3. 3-10 d after spray, the average height and yield increased by 11.50% and 27.56% respectively, in comparison with control. The height increased by 10.59%, 13.33%, 12.71% as for pre-harvest interval (PHI) of 3, 5, 7 d respectively. The yield increased by 33.41%, 44.35%, 17.41% as for PHI of 5, 7, 10 d, respectively. As for PHI of 10 d with low and middle dosage level of GA3, the vitamin C content increased significantly by 67.44% and 44.50% respectively, while the protein content increased by 12.17% and 11.11%, respectively. No significant difference was observed on content of reducing sugar, soluble solids and crude fiber with PHI of 10 d at all three dosage levels of GA3 in comparison with control. The dissipation trend of GA3 in edible amaranth was fitted to a first order kinetics with half-life of 1.24 d. The terminal residues of GA3 in edible amaranth were 0.0012-0.0074 mg/kg with PHI of 5, 7, 10 d under the three application levels, which were far below 0.2 mg/kg, the maximum residue limit (MRL ) of GA3 in edible amaranth in Japan. GA3 was applied at the dosage of 60 g/hm2, when the edible amaranth had 5-6 leaves in summer of Guangzhou, the residue of GA3 was 0.002 mg/kg with PHI of 10 d. Compared with control, the plant yield, vitamin C content and protein content increased by 17.41% , 44.50% and 11.11% respectively. No significant difference was observed on the content of reducing sugar, soluble solids and crude fiber. It is suggested that theMRL of GA3 in edible amaranth from Japan Positive List can be applied in China.