Objective: To compare and analyze the clinical and pathological characteristics between pure mucinous breast carcinoma (PMBC) and mixed mucinous breast carcinomas (MMBC) so as to provide research basis for the diagnosis and treatment of breast mucinous carcinoma (MBC). Methods: Forty patients with MBC were selected as the study subjects, including 25 patients with PMBC and 15 patients with MMBC. The clinical characteristics, the ultrasonographic characteristics, the pathological characteristics of tumor tissues between the two kinds of patients were analyzed retrospectively. Results: The ratio of lymph node metastasis in the patients with MMBC was significantly higher than that in the patients with PMBC, the difference was statistically significant (P<0.05). In the breast ultrasound examinations, the ratios of uneven mass density and abundant blood flow in the patients with MMBC were higher than those in the patients with PMBC, the difference was statistically significant (P<0.05). The histological grading, the nuclear grading, the nuclear mitotic figure score of the tumor tissues of the patients with MMBC were higher than those of the patients with PMBC, the differences between the two groups were statistically significant (P<0.05). There were no significant differences in ER, PR, Her2, Ki-67 positive rates and molecular classification. Conclusion: Compared with PMBC, MMBC shows an increase in the proportion of lymph node metastasis and the characteristics of malignant lesions on ultrasonography. The pathological examination shows the increases of histological grading, the nuclear grading and the nuclear mitotic figure score, which could be used as an important basis for differential diagnosis and treatments.