Primary hyperparathyroidism is typically characterized by monoclonal parathyroid tumors that secrete an excessive amount of parathyroid hormone (PTH). However, the underlying pathogenesis of tumorigenesis remains unclear. We performed single-cell transcriptomic analysis on five parathyroid adenoma (PA) and two parathyroid carcinoma (PC) samples. A total of 63,909 cells were divided into 11 different cell categories;​ endocrine cells accounted for the largest proportion of cells in both PA and PC, and patients with PC had larger populations of endocrine cells. Our results revealed significant heterogeneity in PA and PC. We identified cell cycle regulators that may play a critical role in the tumorigenesis of PC. Furthermore, we found that the tumor microenvironment in PC was immunosuppressive, and endothelial cells had the highest interactions with other cell types, such as fibroblast-musculature cells and endocrine cells. PC development may be stimulated by fibroblast-endothelial cell interactions. Our study clarifies the transcriptional signatures that underlie parathyroid tumors and offer a potential significant contribution in the study of pathogenesis of PC.