In this research,a full-length cDNA sequence of 4CL related to flax lignin synthesis is cloned by RACE-PCR technique on the basis of the segment of this gene cloned freviously.The complete cDNA sequence of 4CL is 1 957 bp in length,with a complete open reading frame of 1 650 bp.The encoded protein contains 549 amino acids,with a molecular mass of 60 kD and a pI of 5.3.Random coil and α-helix are the main secondary structure of the protein.Phylogenetic analysis indicated that there is high similarity between flax 4CL gene and that of Thellungiella halophila.The full-length cDNA sequence has been registered in GenBank,with an accession number of KC832864.A 413 bp CDS fragment of 4CL is amplified by PCR to construct the RNA interference vector p1301M-4CL,which is transformed to flax by agrobacterium-mediated method.Seven transgenic seedlings selected randomly are detected by GUS and PCR.The results showed that the RNAi vector construction has been integrated into flax genome,which leads to evidently depression of the expression of 4CL gene in flax.