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OBJECTIVE To explore the effect of micro-ribonucleic acid (miR)-187 on cisplatin (DDP) resistance of gastric cancer cells by regulating the transforming growth factor-β (TGF-β)/Smad signaling pathway. MATERIALS AND METHODS DDP-sensitivities in GES-1, SGC7901, and SGC7901/DDP cells were detected via Cell Counting Kit-8 (CCK-8) assay. The differential expression of miR-187 of these cell lines was detected by Reverse Transcription-quantitative Polymerase Chain Reaction (RT-qPCR). DDP-resistant gastric cancer cells SGC7901/DDP were divided into control group (blank control), miR-187 inhibitor group (SGC7901/DDP cells transfected with miR-187 inhibitor), and miR-187 mimic group (SGC7901/DDP cells transfected with miR-187 mimic). The protein expressions of miR-187, TGF-β1, p-Smad4, excision repair cross-complementation group 3 (ERCC3), and ERCC4 were determined through RT-qPCR, immunohistochemistry, and Western blotting. The apoptosis in each group was detected by flow cytometry. RESULTS MiR-187 level had a negative correlation with DDP-resistance of GES-1, SGC7901, and SGC7901/DDP cells, and among them, the GES-1 cells had the lowest DDP-resistance and the highest expression of miR-187. CCK-8 assay revealed that compared with that in the control group, DDP-resistance significantly declined in the miR-187 mimic group, while it was significantly enhanced in miR-187 inhibitor group (p<0.01). According to the results of flow cytometry, after treatment with 100 nM DDP for 12 h, the apoptotic rate in miR-187 mimic group enhanced, while it was markedly reduced in the miR-187 inhibitor group (p<0.01). Western blotting and immunohistochemistry results showed that expressions of TGF-β1 and p-Smad4 were significantly downregulated in the miR-187 mimic group, while they were upregulated in the miR-187 inhibitor group (p<0.01). Besides, compared with the control group, ERCC3 and ERCC4 were downregulated in the miR-187 mimic group, while upregulated in miR-187 inhibitor group (p<0.01). CONCLUSIONS The overexpression of miR-187 alleviates DDP-resistance in gastric cancer cells by inhibiting the TGF-β/Smad signaling pathway.