Synthetic food dyes are commonly used to enhance food appearance, yet their potential health risks remain a concern. Green leaf color (GLC), a synthetic dye widely employed in diverse applications such as fashion, product design, and branding, is predominantly used in foods in Bangladesh, where its toxicity has not been comprehensively assessed. This study aimed to investigate the toxicological effects of GLC on growth performance, hematological and biochemical parameters, tissue architecture, and molecular markers in Swiss albino mice. Forty mice were divided into four groups: one control and three treatment groups, receiving oral doses of GLC at 125 (low), 250 (medium), and 500 (high) mg/kg body weight daily for 13 weeks. GLC exposure significantly impaired growth in treated mice and reduced feed efficiency in a dose-dependent manner compared to the controls. Hematological analysis revealed marked reductions in hemoglobin, hematocrit, and MCH, with significant increases in WBC, platelets, and monocyte counts. Biochemical examination showed elevated levels of ALP, ALT, AST, bilirubin, urea, and creatinine. Histological evaluation demonstrated multiorgan damage, including central vein congestion, hepatocellular vacuolization, and inflammatory cell infiltration in the liver; glomerular atrophy, tubular injury, and interstitial edema in the kidney; and villi destruction, epithelial shedding, and mucosal damage in the intestine. At the molecular level, mRNA expression analysis revealed significant upregulation of BCL-2and Beclin-1 genes in the liver, kidney, and intestine, whereas BAX was markedly downregulated in the liver and kidney, and NF-κB expression was suppressed in the intestine, indicating GLC-induced dysregulation of apoptosis and autophagy pathways. This study provides the first comprehensive evaluation of GLC toxicity in mice, integrating biochemical, histological, and molecular evidence. The overall findings demonstrate that GLC induces multilevel toxic effects with potential genotoxic properties. Therefore, strict regulation and preventive measures should be taken to minimize the use of GLC in food products.