BACKGROUND Transcription factor 21 (TCF21), a member of the class A of basic helix-loop-helix family, has been widely identified as a tumor suppressor. Growing evidence has demonstrated the downregulation of TCF21 in distinct cancers. The aim of this study was to explore the expression and biological functions of TCF21 in esophageal squamous cell carcinoma (ESCC). MATERIAL AND METHODS TCF21 expression in esophageal cancer cell lines and carcinomas tissues were detected, and its associations with clinical characteristics were analyzed. We carried out this study of biological functions and underlying mechanisms using TE10 and KYSE510 cell lines. RESULTS TCF21 mRNA and protein expression were both downregulated in esophageal cancer tissues compared with adjacent normal tissues. Low expression of TCF21 was closely correlated with N stage. In Kaplan-Meier survival analysis, patients with lower TCF21 expression had poorer prognosis. Overexpression of TCF21 greatly inhibited the proliferation, migration, and invasion in both TE10 and KYSE510 cell lines. Furthermore, mechanistic studies showed that with TCF21 gene overexpressed, the expression of tumor suppressor Kiss-1 was upregulated and epithelial-mesenchymal transition (EMT) related proteins (E-cadherin, N-cadherin, Snail, Twist, and Vimentin) which participate in cancer cell invasion and metastasis, were reversed. CONCLUSIONS TCF21 is downregulated in ESCC, and its low expression is closely correlated with N stage and predicts a poor prognosis. TCF21 functions as a tumor suppressor in ESCC progression, and enhancement of its expression levels may be partly through promoting Kiss-1 expression to reverse EMT by modulating EMT-related gene expression. Thus, TCF21 can potentially be used as a treatment target for ESCC.