CDS sequence of βcyanoalanine synthase gene (LsCAS) was amplified from the roots of seedlings of Lathyrus sativus germinated for 6 days and expression vector pGEX2TLsCAS was constructed. LsCAS was purified by GST affinity chromatography after induced expression and detected by Westernblot with GST tag antibody and soybean cysteine synthase antibody. The purified LsCAS was digested by thrombin to remove the GSTtag and then the molecular weight was estimated by Superdex 200 Increase 10/300 GL. The results showed that: (1) CDS sequence of LsCAS was 1 035 bp and encoded 344 amino acids; the protein possessed typical CBSlike protein functional domains of cystathionine betasynthase and cysteine synthase. (2) Expression vector pGEX2TLsCAS was successfully constructed and the purified target protein showed a single band with a molecular weight of 64 kD when detected via SDSPAGE; and also, a characteristic band was detected in both induced bacterial proteins and purified recombinant proteins using Westernblot techniques. So, the fusion protein obtained is LsCAS. (3) LsCAS belongs to pyridoxal phosphatedependent cysteine synthetase family because of its characteristic absorption peak at 412 nm; the size exclusion chromatography determining the apparent molecular mass of recombinant LsCAS suggested that LsCAS is tetramer and PLPdependent protease. These results laid a solid foundation for the understanding of LsCAS activity regulation and further functional investigation.