Objective To explore the effects of collagen type Ⅲ α1 (COL3A1) on proliferation, migration, invasion and angiogenesis of breast cancer (BRCA) cells. Methods The GEPIA database was used to analyze the differential expression of COL3A1 in BRCA tissues and normal tissues. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to detect the mRNA expression level of COL3A1 in normal breast epithelial cell (MCF-10A) and BRCA cells. CCK-8 assay, EDU assay, cell scratch assay, Transwell assay and Tube formation assay were used to detect the proliferation, migration, invasion and angiogenesis of BRCA cells, respectively. Western blot was used to detect the expression of COL3A1 and VEGFA proteins in BRCA cells. In vivo, the xenograft tumor model in nude mice was established. Results GEPIA database analysis showed that COL3A1 was high expressed in BRCA tissues compared to normal tissues (P＜0.05). In vitro, compared with sh-NC, COL3A1 knockout significantly inhibited the proliferation, migration, invasion and angiogenesis of MCF-7 and MDA-MB-231 cells (P＜0.01). Compared with sh-NC, COL3A1 knockout significantly down-regulated the protein expression of VEGFA (P＜0.01). In vivo, COL3A1 knockout inhibited the growth of xenograft tumors compared with sh-NC (P＜0.01). Conclusion COL3A1 is highly expressed in BRCA, and the deletion of COL3A1 inhibites the proliferation, migration, invasion and angiogenesis of BRCA cells, which might be a new biomarker for the treatment of BRCA