Extracellular matrix (ECM) remodeling is involved in many cellular properties such as division, migration, differentiation, and death. The turnover of ECM is regulated by matrix metalloproteinases (MMPs) and the MMPs are inhibited by the tissue inhibitors of metalloproteinases (TIMPs). In this study, the transcriptional regulation of the TIMP‐1 promoter was investigated. The 5′‐deletion assay showed that the region between −1,200 and −1,101 was responsible for the TIMP‐1 promoter activity. The mutations of the two Sp1 sites in this region reduced the transcription activity. In addition, the co‐transfection with antisense Sp1 oligonucleotide decreased the promoter activity, suggesting that the transcription of the TIMP‐1 promoter is mediated by Sp1. Previously, it was reported that the TIMP‐1 expression was enhanced under hypoxia. Therefore, the TIMP‐1 promoter activity was investigated with or without cobalt ion, which elicits the same physiological effect as hypoxia. The results showed that the TIMP‐1 promoter was induced in the presence of cobalt ion and that the promoter activity was regulated by Sp1 as well as HIF‐1. Therefore, this study suggests that Sp1 is involved in the regulation of the TIMP‐1 promoter in the presence of cobalt ion as well as in the basal level transcription. © 2004 Wiley‐Liss, Inc.