STUDY QUESTION: Do changes in tumor necrosis factor-α-induced protein 8 (TNFAIP8)-like 2 (TIPE2) levels in endometrium of patients with adenomyosis alter the proliferation, migration and invasion ability of endometrial cells? SUMMARY ANSWER: TIPE2 expression levels were low in eutopic and ectopic endometrium of adenomyosis patients, and TIPE2 inhibited the migration and invasion of endometrial cells, mainly by targeting β-catenin, to reverse the epithelial-mesenchymal transition (EMT). WHAT IS KNOWN ALREADY: Adenomyosis is a benign disease, but it has some pathophysiological characteristics similar to the malignant tumor. TIPE2 is a novel negative immune regulatory molecule, and it also participates in the development of malignant tumors. STUDY DESIGN, SIZE, DURATION: Control endometrium (n = 48 women with non-endometrial diseases) and eutopic/ectopic endometrium from patients with adenomyosis (n = 50), human endometrial cancer cell lines, and primary endometrial cells from the eutopic endometrium of adenomyosis patients were used in the study. PARTICIPANTS/MATERIALS, SETTING, METHODS: The expression level of TIPE2 mRNA and protein in the eutopic/ectopic endometrial tissues of adenomyosis patients and control endometrium was determined by quantitative RT-PCR (qRT-PCR), western blot and immunohistochemistry. The effects of TIPE2 overexpression and knockdown on the proliferation, migration and invasion of endometrial cell lines and primary adenomyotic endometrial cells were determined using a cell counting kit-8, 5-ethynyl-2'-deoxyuridine assay, colony-forming assay, transwell migration assay and matrigel invasion assay. The expression of EMT-related markers and signal molecules was detected by western blot. The interaction between TIPE2 and β-catenin was detected by co-immunoprecipitation and laser confocal microscopy. MAIN RESULTS AND THE ROLE OF CHANCE: The mRNA and protein expression levels of TIPE2 in the eutopic and ectopic endometrial tissues of adenomyosis patients were significantly downregulated compared with the control endometrium (P ˂ 0.01). TIPE2 could bind to β-catenin and inhibit the nuclear translocation of β-catenin, downregulate the expression of stromal cell markers, upregulate the expression of glandular epithelial cell markers, decrease the occurrence of epithelial-mesenchymal transition (EMT) and suppress the migration and invasion of endometrial cells (P ˂ 0.01). LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: In this study, the experiments were performed only in eutopic and ectopic endometrial tissues, endometrial cancer cell lines and primary adenomyotic endometrial cells. A mouse model of adenomyosis will be constructed to detect the effects of TIPE2 in vivo. WIDER IMPLICATIONS OF THE FINDINGS: These results suggest that TIPE2 is involved in the development of adenomyosis, which provides a potential new diagnostic and therapeutic strategy for the treatment of adenomyosis. STUDY FUNDINGS/COMPETING INTEREST(S): This present study was supported by grants from the National Natural Science Foundation of China (81471437, 81771554), Natural Science Foundation of Shandong (ZR2018MH013), Science and technology development plan provided by Health and Family Planning Committee in Shandong (2014-25). The authors declare that they have no conflicts of interest.