Accurate determination of Mebendazole in pharmaceutical formulations is essential for ensuring drug quality and monitoring therapeutic efficacy in humans. Therefore, a new technique for detecting the antifungal medication mebendazole was developed. This method utilizes flow injection analysis with merging zones, offering a quick, straightforward, and highly sensitive approach to quantifying the drug. The method relies on mebendazole to reduce iron III to iron II under acidic conditions. The reduced iron then reacts with 1,10-phenanthroline to form an orange-red colored complex measured spectroscopically at 510 nm. The method showed a linear correlation between response and concentration over 25-250 µg/mL, with 22 and 25.5 µg/mL LOD and LOQ, respectively. The correlation coefficient (r) was 0.9975, indicating excellent linearity. The method was also successfully applied to determine the concentration of mebendazole in tablet formulations, demonstrating its potential for quantitative pharmaceutical analysis. A statistical analysis comparing the results obtained from the newly developed method and established techniques showed no significant discrepancies.