Paeonia ostii seeds have recently been identified as a new source of α-linolenic acid in China. Studying the gene expression patterns of unsaturated fatty acid-related genes would be helpful for understanding the mechanism of α-linolenic acid accumulation. Quantitative real-time polymerase chain reaction (qRT-PCR) is a useful method for reliably evaluating gene expression, and it is necessary to select reliable reference genes for data normalization in qRT-PCR analysis. In this study, we evaluated the expression stability of 12 candidate reference genes using four mathematical algorithms (∆Ct, BestKeeper, NormFinder, and geNorm). The web-based tool RefFinder was used to integrate the results and to provide a comprehensive ranking order. The expression stability ranking orders of reference genes were different caculated by these four algorithms, and the ranking order analyzed by the RefFinder was UBQ > Tip41 > UCE > EF-1α > α-TUB > PP2A > ACT > GAPDH > SAM > CYP > β-TUB > 18S at the different seed development stages, and UBQ > Tip41 > EF-1α > α-TUB > PP2A > UCE > GAPDH > SAM > ACT > CYP > 18S > β-TUB in P. ostii tissues. UBQ and Tip41 are the two most stable whereas 18S and β-TUB are the two least stable reference genes for gene expression in various tissues and seeds at different developmental stages in P. ostii.