TRAP, a characteristic marker of osteoclast differentiation, is an enzyme that plays an active role in the process of bone resorption. Despite the importance of TRAP in osteoclast biology, the components involved in the transcriptional regulation of this gene are largely unknown. This study investigated the regulation of TRAP transcription by the Myc oncoprotein in three different cell types. A series of nested TRAP promoter deletion constructs were cotransfected into P388D₁ murine macrophages and C3H10T1/2 murine embryonic fibroblasts along with a backbone plasmid control or expression plasmids containing v‐Myc, c‐Myc, or an inactive v‐Myc protein construct (Δ84/NLS). Both v‐Myc and c‐Myc negatively regulated transcription from the TRAP promoter in P388D₁ and C3H10T1/2 cells, 90% and 50%, respective to cell type and amount of endogenous Myc protein, and Δ84/NLS had no effect. The functional Myc‐responsive element(s) within the TRAP promoter was localized to a region between −436 and +1 bp, which contains two putative Myc‐inhibitory binding sites coincident with an initiator element (Inr) at −116 bp and −18 bp. Conversely, in the HD‐11EM chicken v‐Myc transformed preosteoclast cell line, the full‐length TRAP promoter transcription was increased when endogenous v‐Myc levels were decreased in response to pretreatment of these cells with 1α,25‐dihydroxyvitamin D₃ [1α,25(OH)₂D₃]. This report provides the first evidence of the specific regulation of TRAP at the transcriptional level by Myc, a transcription factor that is normally expressed at relatively high levels in preosteoclasts and other myelomonocytic cells and suggests that Myc plays an active role in suppressing the transcription of a mature osteoclast selective gene.