Our findings provide several insights into the underlying mechanisms and potential strategy for enhancing 5-FU chemosensitivity in breast cancer: (1) SNORD3A as an lncRNA is downregulated in breast cancer (2) resulting from downregulation of the Meis1 transcription factor and (3) SNORD3A acts as a ceRNA of miR-185-5p (4) to upregulate UMPS protein expression and specifically enhance chemosensitivity to 5-FU. This evidence concerns the gene UMPS and breast carcinoma.