Colorectal cancer (CRC) remains a crucial health problem due to the toxicity of 5-Fluorouracil (5-FU) as first-line chemotherapy agent for treating CRC. The anticancer effects of boron and its compounds have been shown in various cell lines. This study aimed to examine the cytotoxic and apoptotic effects of borax (sodium tetraborate) alone or along with 5-FU on human CRC cells, DLD-1. Cytotoxicity and apoptosis were determined by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay, 4',6-diamidino-2-phenylindole and annexin V/propidium iodide staining. The results showed that combined treatment revealed a significant time- and concentration-dependent cytotoxic effect on DLD-1 cells compared with borax or 5-FU treatment alone. The combination of borax and 5-FU induced a clear increase in the early apoptotic cell percentage, compared to the cells treated with monotherapies. Additionally, a significant increase in condensed and fragmented nuclei was detected in DLD-1 cells treated with the combination treatment compared with borax or 5-FU alone. Our current findings suggest that the combination of borax with 5-FU has a strong cytotoxic and apoptotic effect on the human CRC DLD-1 cells.