Background <p>Ovarian steroid cell tumors-not otherwise specified (SCT-NOS) is a rare category of sex cord-stromal tumor, however, its pathophysiology is unclear. A comprehensive cellular atlas of ovarian SCT-NOS remains lacking.</p> Methods <p>We reported a case of a 41-year-old woman with hyperandrogenism for whom histopathological analysis confirmed the presence of ovarian SCT-NOS. This study utilized single-cell RNA sequencing in a case of ovarian SCT-NOS.</p> Results <p>Seven cell types, including four keratin 19 (KRT19)⁺ steroidogenic cell subtypes, were identified in the tumor microenvironment. We detected aberrant gene expression across various cell types in ovarian SCT-NOS. KRT19⁺ steroidogenic cells were enriched in genes involved in ovarian steroidogenesis and steroid biosynthesis pathways, which was consistent with the pathobiology of hyperandrogenism. Moreover, we revealed distinct immune cell types in the tumor microenvironment. Five immune cell types within the tumor microenvironment were identified, among which tumor-associated macrophage (TAM) and dendritic cell (DC) were the predominant immune cells.</p> Conclusions <p>This transcriptomic analysis revealed distinct cell types and key genes within the tumor microenvironment, offering insights into the cellular heterogeneity and molecular mechanisms of ovarian SCT-NOS, thereby enhancing the understanding and encouraging further investigations into ovarian SCT-NOS.</p>