Abstract: Aconitum pendulum is a Tibetan medicine that is rich in bioactive compounds such as aconitine-type C₁₉-diterpenoid alkaloids. To investigate the key enzymes in the aconitine biosynthesis pathway, roots, leaves and flowers of Aconitum pendulum were subjected to a high-throughput transcriptomic sequencing analysis by Illumina HiSeq^TM2000. Trinity de novo assembly yielded 47 264 unigenes with an average length of 1 140 bp and N50 of 1 678 bp, of which 30 231 unigenes (63.96%) were annotated. In the KEGG database, 542 unigenes were implicated in 17 secondary metabolic pathways; the analysis showed that 44 genes encoded 20 key enzymes in the diterpene skeleton of aconitine biosynthesis and 12 BAHD acyltransferase genes were related to the acetylation modification, with differential expression among three organs. For example, ApTPS8 was the only committed enzyme in the upstream aconitine biosynthetic pathway. The high expression level of ApTPS8 in root indicated that it is the main tissue for the production of precursors of diterpene alkaloids. Consistent with the accumulation of aconitine, we propose that ApBAHD1/2/8 is involved in the biosynthesis of 2-hydroxyaconitine, dehydrated 14-benzoylaconitine, 8-O-methyl-14-benzoylaconine, benzoyldeoxyaconitine and benzoylaconitine, and ApBAHD10 is involved in the biosynthesis of acontine, lucidusculine, 14-O-acetylneoline and 14-O-acetylvirescenin. Comparative transcriptome analysis of A. pendulum and A. carmichaeli indicates significant gene loss in the family of diterpene synthases and acyltransferases in A. pendulum, which is in accordance with the significantly fewer type and quantity of aconitine compounds in this species. Therefore, A. pendulum has proved to be an ideal material for the study of the aconitine biosynthesis pathway. This work provides basic scientific data for further study of aconitine biosynthesis, the discussion of molecular mechanisms of toxicity, and the synthesis of genuine medicinal materials.