Few studies have investigated the role of extracellular-matrix proteoglycans in the pathogenesis of drug-induced gingival overgrowth (DIGO). SPOCK1 is an extracellular proteoglycan that induces epithelial to mesenchymal transition (EMT) in several cancer cell lines and exhibits protease-inhibitory activity. However, the role of SPOCK1 in non-cancerous diseases such as DIGO has not been well-addressed. We demonstrated that the expression of SPOCK1, TGF-β1, and MMP-9 in calcium channel blocker-induced gingival overgrowth is higher than that in non-overgrowth tissues. Transgenic mice overexpressing Spock1 developed obvious gingival-overgrowth and fibrosis phenotypes, and positively correlated with EMT-like changes. Furthermore, in vitro data indicated a tri-directional interaction between SPOCK1, TGF-β1, and MMP-9 that led to gingival overgrowth. Our study shows that SPOCK1 up-regulation in a noncancerous disease and SPOCK1-induced EMT in gingival overgrowth occurs via cooperation and crosstalk between several potential signaling pathways. Therefore, SPOCK1 is a novel therapeutic target for gingival overgrowth and its expression is a potential risk of EMT induction in cancerous lesions.