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The biosynthetic pathways of phytosterols and steroidal saponins are located in two adjacent branches which share cycloartenol as substrate.The rate-limiting enzyme S-adenosyl-L-methionine-sterol-C24-methyltransferase 1 (SMT1), facilitates the metabolic flux towards phytosterols.It catalyzes the methylation of the cycloartenol in the side chain of the C24-alkyl group to generate 24(28)-methylene cycloartenol.In this study, we obtained two full-length sequences of SMT1 genes from Pari polyphylla, designated PpSMT1-1 and PpSMT1-2.The full-length cDNA of PpSMT1-1 was 1369 bplongwith an open reading frame (ORF) of 1038 bp, while the PpSMT1-2 had a length of 1222bp, with a 1005 bpORF.Bioinformatics analysis confirmed that the two cloned SMTs belong to the SMT1 family.The predicted function was further validated by performing in vitro enzymatic reactions, and the results showed that PpSMT1-1 encodes a cycloartenol-C24-methyltransferase, which catalyzes the conversion of cycloartenol to 24-methylene cycloartenol, whereas PpSMT1-2 lacked this catalytic activity.The tissue expression patterns of the two SMTs revealed differential expression in different organs of Paris polyphylla plants of different developmental stage and age.These results lay the foundation for detailed genetic studies of the biosynthetic pathways of steroid compounds, which constitute the main class of active substances found in Paris polyphylla.