Breast cancer (BC) is the most frequent tumor and the leading cause of cancer death in women worldwide. Triple-negative breast cancer (TNBC) is the histologic subtype with the worst prognosis and fewest therapeutic options. MiRNAs are small non-coding RNAs that regulate gene expression. Aberrant expression of miRNAs in body tissues are linked to pathologies like BC. Using bioinformatic approaches, we identified miRNAs whose expression is altered in BC tissue and correlates with patient survival, such as miR-28-3p and miR-28-5p, which are decreased in BC tissue compared to adjacent normal tissue. Our aim was to investigate the effect of miR-28-3p/5p in TNBC. The hypothesis is that miR-28-3p/5p have tumor suppressor functions in TNBC. We determined miR-28 expression levels in PAM50 basal-like BC tumors and normal mammary tissue (NT) from TCGA BRCA and GTEx project data sets. We found that miR-28-5p was significantly increased in basal-like BC tissue compared to NT. Analysis using UCSC Xena showed that miR-28-3p/5p expression is increased in basal-like BC compared to the other PAM50 BC subtypes. Expression of miR-28-3p correlates with higher disease free interval and progression free interval of basal-like BC patients. To investigate the effect of mir-28 in TNBC, we generated stable-transfected 4T1 cells with an expression vector from this miRNA or control (pSGIPX). We evaluated the effect of the miRNAs in proliferation, clonogenicity, adhesion and migration through in vitro assays. We found that miR-28-3p/5p decreased cell viability, migration and adhesion, and clonogenic assay demonstrated that they decreased both the number and size of clonogenic foci. Our results suggest that miR-28-3p/5p could have potential therapeutic implications limiting TNBC cells ability to proliferate and spread by impairing the proliferation, clonogenic capability, adhesion and migration of TNBC cells.