Chalcone synthase is a key factor to flavonoids synthesis.AcCHS1 and AcCHS2,the two chalcone synthase genes,were cloned from onion.The open reading frame(ORF) of AcCHS1 gene contained 1 182 bp encoding a protein of 393 amino acids and the ORF of AcCHS2 gene contained 1 176 bp encoding a protein of 391 amino acids.Under the same conditions,the expression of AcCHS2 was higher than that of AcCHS1.