Objective To evaluate the possible causes of misdiagnosis of minimal breast carcinoma (MBC). Meth-ods The possible causes of misdiagnosis of 90 cases of MBC confirmed by pathology were retrospective analyzed. Accord-ing to the maximum diameter of the lesion, 90 cases were divided into 0.5-1.0 cm group (n=55) and≤0.5 cm group (n=35). And these two groups were subdivided into correct and misdiagnosed groups. The two-dimensional ultrasound findings were observed by using SIEMENZ S2000, GE vivid7 and GE vivid9 color Doppler ultrasound instruments, and reasons of misdiag-nosis were analyzed. Results There were 32 cases were misdiagnosed in 90 patients with MBC. There was significant differ-ence in boundary of misdiagnosis between diameter 0.5-1.0 cm group and≤0.5 cm group. There were significant differences in boundary and calcification between misdiagnosed group and correct group in diameter 0.5-1.0 cm group (P<0.05). There were also significant differences in A/T ratio and accompanying by multiple benign nodules between misdiagnosed group and correct group in diameter≤0.5 cm group (P<0.05). Conclusion The misdiagnosis in MBC is because of different lesion sizes. The misdiagnosis happens in the maximum diameter of the lesions between 0.5-1.0 cm that showed manifestation of sharp edges, no micro-calcification in sonographic features of benign. The misdiagnosis happens in maximum diameter of le-sions≤0.5 cm that manifested as the aspect A/T ratio<1 and characterized by multiple nodules.