Invasive micropapillary carcinoma (IMPC) is an uncommon histological type of breast cancer. IMPC has a special growth pattern and a more aggressive behavior than invasive ductal carcinomas of no special types (IDC-NSTs). microRNAs are a large class of non-coding RNAs involved in the regulation of various biological processes. Here, we analyzed the small RNA transcriptomes of five formalin-fixed paraffin-embedded (FFPE) pure IMPC samples and five FFPE IDC-NSTs samples by means of next-generation sequencing, generating a total of >170,000,000 clean reads. In an unsupervised cluster analysis, differently expressed miRNAs generated a tree with clear distinction between IMPC and IDC-NSTs classes. Paired fresh-frozen and FFPE specimens showed very similar miRNA expression profiles. By means of RT-qPCR, we further investigated miRNA expression in more IMPC (n = 22) and IDC-NSTs (n = 24) FFPE samples and found let-7b, miR-30c, miR-148a, miR-181a, miR-181a*, and miR-181b were significantly differently expressed between the two groups. We also elucidated several features of miRNA in these breast cancer tissues including 5' variability, miRNA editing, and 3' untemplated addition. Our findings will lead to further understanding of the invasive potency of IMPC and gain an insight into the diversity and complexity of small RNA molecules in breast cancer tissues.