The stearoylACP desaturase (SAD) gene from Paeonia ostii was cloned using RTPCR and RACEPCR strategies, named as PoSAD (GenBank accession number: KY038819). The full length of FAD3 cDNA is 1 559 bp, contains a 1 197 bp open reading frame (ORF) encoding a putative protein of 398 amino acids. The noncoding districts of 3′ and 5′ end are 172 bp and 123 bp. Multiple sequence alignment results showed that it contains two conserved domains of PoSAD gene. Phylogenetic tree analysis showed that the P. ostii had the closest evolutionary relationship with Ricinus communis. Subcellular localization analysis of TMHMM and TargetP indicated that it might be targeted to the endoplasmic reticulum without transmembrane region. PoSAD gene was expressed in the root, stem, leaf, petal, pistil, stamen and seed of P. ostii by the tissuespecificity expression. The expressive content of PoSAD gene in different tissues of P. ostii was different: the highest was petal, the next was pistil, and the lowest level was in root; in different periods of seeds, the highest expression was in seeds of 60 d, the next was 80 d. The expression level of 10 d was the lowest.