【Objective】 The aims of the study is to figure out the role of acyl-CoA synthetase in dencicine (β-N-oxalyl-L-α, β-diaminopropionic acid, β-ODAP) biosynthesis. 【Methods】acyl-activating enzyme (AAE) superfamily genes were identified in the genome of grass pea (Lathyrus sativus L.) using the AMP binding domain hidden Markov model. After that, the acyl-CoA synthase gene was cloned and analyzed via multiple sequence alignment, prokaryotic expression and enzyme activity detection. 【Results】 The results showed that not less than 22 AAE family genes were located on 7 different branches in grass pea; phylogenetic analysis indicated that LsAAE3 and AtAAE3 (Arabidopsis thaliana) gathered to one branch and be subsumed to acyl-CoA synthetase family. Cloning and sequence analysis manifested that the full-length cDNA of LsAAE3 was 1 566 bp, LsAAE3 and AtAAE3 possessed several conversed domains including AMP binding site, CoA binding site and AAE consensus motif. The purified protein of which molecular weight was 56 kD showed a single band via SDS-PAGE, while the same band was also detected in both induced bacterial proteins and purified recombinant proteins by Western blot, both of which suggested that the fusion protein we obtained was LsAAE3. The oxaloyl-CoA synthase activity of LsAAE3 depended on ATP and magnesium ions.【Conclusion】 In conclusion, the study identified acyl-activating enzyme (AAE) superfamily genes in the genome of grass pea and verified the oxaloyl-CoA synthase activity of LsAAE3, which paved the way for further analysis of the function of LsAAE3 in β-ODAP biosynthesis.