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OBJECTIVE The purpose of this study was to explore the expression and biological functions of long non-coding ribonucleic acid (lncRNA) ribonuclease P RNA component H1 (RPPH1) in gastric cancer (GC), and to analyze the correlations of lncRNA expression with the clinical features and prognosis of GC patients. PATIENTS AND METHODS The relative expression of RPPH1 in tissue specimens from 60 GC patients was measured via quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR), and the correlations of RPPH1 expression with tumor-node-metastasis (TNM) stage, lymph node metastasis, etc. in GC patients were analyzed. Then, qRT-PCR was performed to detect the relative expression level of RPPH1 in GC cells. Moreover, colony formation assay, 5-Ethynyl-2'-deoxyuridine (EdU) staining, wound-healing assay, and transwell assay were employed to investigate the influence of RPPH1 on GC cell functions. After interfering in the expression of RPPH1, the changes in p21 (CDKN1A, cyclin dependent kinase inhibitor 1A) expression were determined through qRT-PCR and Western blotting. RESULTS It was shown in qRT-PCR assay results that the expression of RPPH1 was upregulated in 60 cases of GC tissues. Statistical analysis revealed that RPPH1 expression was positively correlated with the TNM stage, lymph node metastasis, and infiltration depth in GC patients. Besides, highly expressed lncRNA RPPH1 suggested poor prognosis of GC patients. Based on the results of qRT-PCR assay, the expression of RPPH1 in GC cells was upregulated. After interfering in RPPH1 expression, both colony formation assay and EdU staining indicated that the proliferative capacity of GC cells was repressed. Furthermore, it was manifested in the results of wound-healing and transwell assays that the migratory and invasive abilities of GC cells were weakened. Finally, the qRT-PCR and Western blotting assay results demonstrated that p21 expression was upregulated after interfering in the expression of RPPH1 in GC cells. CONCLUSIONS The expression of lncRNA RPPH1 is upregulated in GC, suggesting that the prognosis of the patients is poor. Highly expressed RPPH1 promotes the proliferation and metastasis of GC cells by regulating p21 expression.