Objective:To investigate relationships between nasal parasitism by Demodex mites and nasal skin microbiome in patients with rosacea. Methods:From May 2017 to June 2019, 14 patients with rosacea, including 8 with early-stage rosacea and 6 with intermediate-stage rosacea, and 14 human controls with healthy facial skin were collected from Department of Dermatology, Shunde District Center for Prevention and Cure of Chronic Disease of Foshan City. Microbial samples were collected from the nasal alar and nasolabial folds of the subjects. Then, DNA was extracted from the samples, and subjected to metagenomic sequencing and bioinformatics analysis. Relative abundance of strains was estimated by using composition ratios of Demodex mites and microbial reads. Shannon index was calculated to evaluate α diversity of microbiome, and principal component analysis (PCA) was performed to assess β diversity based on relative abundance of microbial species. Enumeration data were compared by using two-independent-sample t test, and relationships between nasal Demodex mites and skin microbiome were analyzed by Pearson correlation analysis. Results:The relative abundance of nasal Demodex mites was significantly higher in the rosacea group (1.647% ± 0.389%) than in the healthy group (0.448% ± 0.089%, t = 2.92, P = 0.007) . The relative abundance of Demodex mites was negatively correlated with the relative abundance of bacteria ( r = -0.95, P < 0.001) , and positively correlated with the relative abundance of fungi ( r = 0.76, P < 0.001) . The Shannon indices of nasal bacterial and fungal communities were significantly higher in the rosacea group (0.91 ± 0.17, 1.261 ± 0.045, respectively) than in the healthy group (0.47 ± 0.12, 0.549 ± 0.071, t = 2.17, 8.48, respectively, both P < 0.05) ; PCA showed that the β diversity of bacterial communities significantly differed between the rosacea group and healthy group ( t = 2.32, P = 0.029) , while no significant difference in the β diversity of fungal communities was observed between the two groups ( t = 0.82, P = 0.461) . In addition, the relative abundance of Demodex mites was significantly higher in the patients with intermediate-stage rosacea than in those with early-stage rosacea ( t = 6.56, P < 0.001) ; there was no significant difference in the Shannon indices of nasal bacterial or fungal communities between the two patient groups (both P > 0.05) ; PCA showed that the β diversities of bacterial and fungal communities significantly differed between the two patient groups (both P < 0.05) . Conclusion:Parasitism of Demodex mites on the nasal skin may affect nasal microbial community structure.