One of the main chemotherapy agents for colon cancer is 5-fluorouracil (5-FU). However, the effectiveness of 5-FU decreased; therefore, co-chemotherapy with another agent is needed to enhance the activity. This study aims to determine the effect of red ginger extract as a co-chemotherapy agent with 5-FU on WiDr colon adenocarcinoma cells. We investigated the cytotoxic activity of the ethanolic extract of rhizome red ginger and combination with 5-fluorouracil (5-FU) in WiDr human colorectal cancer cell line. Red ginger extract was extracted by using 96% ethanol. Cytotoxic assay of red ginger extract and 5-FU was performed using MTT assay for 24 and 48 hours. Treatment of 5-FU in WiDr cells for 48 hours showed an IC50 value of 130 µg/mL, while no IC50 value was obtained for the 24 hours treatment. Treatment of red ginger extract with an incubation time of 24 and 48 hours had a cytotoxic effect on WiDr cells with IC50 values of 68 µg/mL and 65 µg/mL, respectively. The combination of 1000 μg/mL 5-fluorouracil with 35 μg/mL red ginger extract at 24-hour incubation resulted in a smaller cell viability value than every single treatment. The combination treatment of 5-FU 60 μg/mL with red ginger extract at a 25 μg/mL concentration causes a more significant decrease in cell viability than a single 5-FU treatment. In conclusion, red ginger extract may increase the cytotoxic activity of 5-FU in colon adenocarcinoma WiDr cells.