The oncogenic role of lncRNA MCM3AP-AS1 has been reported in several types of cancer, while its role in triple negative breast cancer (TNBC) is unknown. The expression levels of MCM3AP-AS1 and MEG3 in TNBC and paired nontumor tissues from 60 TNBC patients were measured by RT-qPCR. The effects of overexpres-sion of MCM3AP-AS1 and MEG3 on the proliferation of BT-20 and BT-549 cells were evaluated by cell proliferation assay. We found that MCM3AP-AS1 was upregulated in TNBC, while lncRNA MEG3 was downregulated in TNBC, and they were inversely correlated with each other. In addition, the expression levels of MCM3AP-AS1 increased with the increase in tumor size, while the expression levels of MEG3 decreased with the increase in tumor size. In TNBC cells, overexpression of MCM3AP-AS1 led to downregulated expression of MEG3, while overexpression of MEG3 did not affect the expression of MCM3AP-AS1. Cell proliferation analysis showed that overexpression of MCM3AP-AS1 led to increased cell proliferation rate and reduced the inhibitory effects of overexpression of MEG3 on cancer cell proliferation. Therefore, MCM3AP-AS1 downregulates MEG3 in TNBC to inhibit the proliferation of cancer cells.