Owing to the high prevalence of periodontitis and its impact on quality of life, a rigorous characterization of periodontal tissue is necessary. However, this has previously been impeded by the cellular heterogeneity of periodontal tissue. Here, we characterized the gene expression of gingival tissue in health and periodontitis at single-cell resolution. We reported the loss of epithelial homeostasis-associated genes expressed by specific epithelial cell types in periodontitis. We detected endothelial cells highly associated with immune regulation and fibroblasts potentially involved in bone remodeling. We revealed the myeloid cells with diverse clusters dominated by pro-inflammatory phenotype. We further identified cell subtypes specifically expressing periodontitis related genes and highlighted the cell-cell communication alteration between conditions. This novel single-cell study generated a comprehensive catalog of cells types and interaction networks in the human gingiva for the first time, thus offering deeper insights into the biological foundation of periodontal homeostasis and diseases, which will be helpful in advancing periodontal diagnosis and therapy.