The anti-carcinogenic effect of Methylglyoxal (MG) is well established. It generally targets malignant cells by affecting glycolysis and mitochondrial respiration with minimum or no toxicity to normal cells. In an initial study we have reported that MG can synergistically act with 5-Fluorouracil (5-FU) to decreases the number of MCF-7 breast cancer cells (Ghosh S, Pal A, Ray M, 2017). This finding prompted us to study the combination effect of MG and 5-FU extensively in both in vitro and in vivo. Induction of cell apoptosis and cell cycle arrest was systematically studied to reveal the mechanisms of synergy between 5-FU and MG. Our present study revealed that MG can synergistically act with 5-FU and can cause cell death via apoptosis and generated reactive oxygen species (ROS) in MCF-7 cells. Combination of 5-FU and MG resulted in more potent apoptosis induction as revealed by fluorescence microscopy using Hoechst 33342. In comparison to single drug treatment, the co-treatment also increased the number of cells in G0/G1 phase by downregulating the expression of CDK4 and CDK6 as compared to single drug treatment. Levels of Caspase 9 and poly (ADP-ribose) polymerase (PARP) were higher in combination treatment as compared to single drug treatment. These results clearly showed that 5-FU is more effective at lower doses in presence of MG in MCF-7 cells. In case of in vivo studies treatment of EAC (Ehrlich Ascites Carcinoma) bearing mice with MG in combination with 5-FU at various doses, demonstrated the same synergistic effect of MG with 5-FU. The combination study also exhibited tumor regression in BALB/c mouse 4T1 breast tumor model as well. We also clearly demonstrated that MG can decrease the cytotoxic side effects of 5-FU as indicated with acute and chronic toxicity studies and other biochemical analyses of blood and histological studies. Taken together, our results revealed that MG could be a potential candidate for combination therapy to reduce the toxicity burden of 5-FU without any toxic impact on host cells.