Spi-C is an E26 transformation-specific transcription factor closely related to PU.1 and Spi-B. Spi-C has lineage-instructive functions important in B cell development, Ab-generating responses, and red pulp macrophage generation. This research examined the regulation of Spi-C expression in mouse B cells. To determine the mechanism of Spic regulation, we identified the Spic promoter and upstream regulatory elements. The Spic promoter had unidirectional activity that was reduced by mutation of an NF-kB binding site. Reverse transcription-quantitative PCR analysis revealed that Spic expression was reduced in B cells following treatment with cytokines BAFF + IL-4 + IL-5, anti-IgM Ab, or LPS. Cytochalasin treatment partially prevented downregulation of Spic. Unstimulated B cells upregulated Spic on culture. Spic was repressed by an upstream regulatory region interacting with the heme-binding regulator Bach2. Taken together, these data indicate that Spi-C is dynamically regulated by external signals in B cells and provide insight into the mechanism of regulation.