Objective To investigate the expression and significance of microRNA-21 (miRNA-21) and its target gene Pellino-1 (Peli1) in mouse model of autoimmune premature ovarian insufficiency (POI).Methods Twenty-four female BALB/c mice were randomly divided into POI group and control group (12 in each group), with zona pellucida 3 (ZP3) polypeptide and the same dose of normal saline subcutaneously injected, respectively. Ovarian function was evaluated by counting follicles, observing estrus cycle and detecting the levels of serum estradiol, follicle-stimulating hormone (FSH) and anti-Müllerian hormone (AMH). The levels of interferon-γ and interleukin (IL)-10 were detected by enzyme-linked immunosorbent assay, the ratio of regulatory T cells (Tregs) of the spleen was detected by flow cytometry, the target gene of miRNA-21 was predicted by bioinformatics, and the expression of miRNA-21 in peripheral blood mononuclear cells (PBMCs) and ovarian tissues and the mRNA expression of Peli1 in PBMCs and Tregs of the spleen were detected by quantitative polymerase chain reaction.Results Six weeks after the second immunization, the mice in the POI group basically had no estrus, while the estrus cycle was normal in the control group. The number of follicles of each grade in the ovaries, the levels of serum estradiol, AMH and IL-10, ratio of Tregs in the spleen, and the expression levels of miRNA-21 in PBMCs and ovarian tissues were significantly lower in the POI group than those in the control group (all P < 0.05), while the levels of serum FSH and interferon-γ were significantly higher than those in the control group (both P < 0.01). Bioinformatics prediction revealed that Peli1 was a target gene of miRNA-21. The mRNA expression levels of Peli1 in PBMCs and splenic Tregs in the POI group were significantly lower than those in the control group (all P < 0.05).Conclusion The expression of miRNA-21 and its target gene Peli1 is significantly decreased in autoimmune POI mouse model, suggesting that miRNA-21 and Peli1 may be involved in the pathogenesis of autoimmune POI.