Backgroud/Aims: Mesenchymal stromal cells (MSCs) are a major component of the tumor microenvironment (TME). Several studies focusing on tumor-derived MSCs have demonstrated that they exhibit a strong ability to promote the tumor epithelial-mesenchymal transition (EMT). However, the factors mediating these effects are poorly understood. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemistry assays were used to detect the expression of Gremlin1 (GREM1) in human esophageal squamous cell carcinoma (ESCC) tissues. ShRNA silencing, flow cytometry, cell counting kit (CCK8) assay, invasion assay, western blot were used to detect the effect of GREM1 in ECa109, TE-1 cell lines and xenograft tumor models. In the current study, we found that the GREM1 was overexpressed in human ESCC tissues. The conditioned medium from mesenchymal stromal cells (MSCs-CM) enhanced the malignancy of xenograft esophageal tumors in vivo, as well as the cell proliferation, viability and invasion of the esophageal carcinoma cell lines ECa109 and TE-1 in vitro. Furthermore, the shRNA silencing of GREM1 in MSCs (shGREM1-MSCs) reversed the increased malignancy of the esophageal tumor in vivo, while the conditioned medium from shGREM1-MSCs (shGREM1-MSCs-CM) affected the cell cycle and cell invasion in vitro. These processes were accompanied by the EMT in the ECa109 and TE-1 cell lines with an alteration in the expression levels of mesenchymal and epithelial markers. Furthermore, the TGF-β/BMP (transforming growth factor-beta/bone morphogenetic protein) signaling pathway participated in the shGREM1-MSCs-CM-induced anti-tumor effect on enhanced esophageal malignancy induced by MSCs-CM treatment. Taken together, our study suggested that GREM1 delivered by MSCs promoted EMT in ESCC in vitro and in vivo, which is partly through TGF-β/BMP signaling pathway. The results provide experimental evidence to a potential therapeutic target in the treatment of esophageal cancer. © 2018 The Author(s). Published by S. Karger AG, Basel.