The fission yeast Schizosaccharomyces pombe is a useful model organism for studying a variety of eukaryotic cellular events such as the cell cycle control mechanisms. For inducible expression of exogenous genes in S. pombe, vectors carrying the nmt1 (no message in thiamine 1) promoter are most commonly used. Although nmt1 is a potent promoter, its transcription activity is drastically repressed in the presence of a low concentration of thiamine. Therefore, a combination of thiamine and nmt1 promoter is convenient for regulating gene expression in an all-or-none fashion. However, it has been difficult to adjust the nmt1 promoter activity in a controlled manner. Here we describe a chemical compound, designated as YAM2, whose repressive activity on the nmt1 promoter has a wider linear range than thiamine. Expression of exogenous proteins, such as human immunodeficiency virus type 1 Vpr and jellyfish green fluorescent protein, driven by the nmt1 promoter is gradually repressed by YAM2 in a dose-dependent manner. YAM2 does not exhibit a detectable level of cytotoxicity at a concentration required to fully repress the nmt1 promoter. The compound may serve as a useful tool for controlled expression of the nmt1-driven gene in S. pombe.