This research investigates a sensitive quantitative estimation of metronidazole (MZOL) in each of its pharmaceutical preparations and its level in human blood with one color reaction and one simple spectrophotometric technique. Metronidazole the antibiotic and antiprotozoal medication is determined by the reduction reaction of MZOL to 2-(2-Methyl-5-amino-1H-imidazole-1-yl) ethanol, followed by coupling with diazotized p-amino benzophenone (PABPh) reagent. The produced color complex is measured at 431 nm. The proposed method is successfully applied for the determination of metronidazole in different dosage forms (tablet, suspension, and intravenous injection) with high precision (RSD% from ±0.011 to ±2.3). as well as it applied for the determination of metronidazole in human blood samples of healthy voluntaries easily and accurately after 4, 6, 12, and 24 hours of oral administration with relative standard deviation not more than ±1.922 which provide the ability for therapeutic monitoring follow up of metronidazole in blood.