Objective: To explore the regulatory mechanism of RNPC1 on the expression of Snail family transcriptional repressor 1 (Snail) in BT474 breast cancer cells and the possible role of RNPC1 in breast cancer lymph node metastasis. Methods: Immunohistochemical (IHC) staining was used to detect and compare the expression of RNPC1 in 42 cases of breast cancer tissues with lymph node metastasis and 39 cases without lymphatic metastasis. The difference of RNPC1 gene level in breast cancer tissues with or without lymph node metastasis was calculated via utilizing TCGA database. The expression of RNPC1 in BT474 cells was knocked down or induced by lentiviral vector, and the effect was identified by qRT-PCR and Western blot. Dual-luciferase activity assay was applied to test and verify the target gene of RNPC1. Results: Compared with breast cancer tissues with lymph node metastasis, expression of RNPC1 was significantly higher in those without lymph node metastasis. The qRT-PCR and Western blot results showed that knockdown of RNPC1 in BT474 cells up-regulated Snail levels, whereas overexpression of RNPC1 resulted in down-regulation of Snail expressions. The dual-luciferase activity assay confirmed that 3′-untranslated region (3′-UTR) was required for RNPC1 to decrease the expression of Snail. Conclusion: Our findings suggested that RNPC1 might inhibit breast cancer metastasis via targeting Snail.