Metastasis in invasive carcinoma is closely associated with the production of extracellular matrix catabolic enzymes, such as matrix metalloproteinases (MMPs). It is known thatetsproto-oncogenes exist in transcriptional regulation refions of the MMP gene and enhance or inhibit MMP transcription. In this study, we restrained theets-1 gene expression of an oral squamous carcinoma cell line by means of RNA interference (RNAi) and examined the change in invasion ability from a molecular biological perspective. An oral squamous carcinoma cell line (HSC-3) was transfected with short interfering RNA (siRNA) ofets-1. The invasive ability of the transfected cells was determined by a matrigel invasion assay, and MMP-9 production was measured by gelatin zymography. These data were compared with those of normal cultured cells. Matrigel invasion assay demonstrated that the transfected cells had a lower invasive ability than HSC-3, and gelatin zymography demonstrated that the MMP-9 production in these cells had decreased. These results suggested that transfection of siRNAets-1 would inhibit tumor invasion through down-regulation of MMP-9.