A simple, inexpensive and reagent-less colorimetric micro flow analysis ([mu]FA) system was implemented in a polymethyl methacrylate (PMMA) micro fluidic manifold. A T-shaped micro channel on a PMMA chip was fabricated by laser ablation and topped with molded polydimethylsiloxane (PDMS). The fabricated [mu]FA system was integrated with the optical components as detector and applied to the determination of iron in water samples. It is based on the measurement of Fe(III)-nitroso-R salt complex at 720 nm formed by the reaction between Fe(III) and nitroso-R salt in an acetate buffer solution pH 5. The proposed [mu]FA consumed very small amount of reagent and sample, it released waste of less than 2.0 mL h-1. The relative standard deviation (R.S.D.) was less than 2% (n = 11) with the recovery of 98.7 ฑ 0.12 (n = 5). The linear range for the determination of iron in water samples was over the range of 0.05-4.0 [mu]g mL-1 with a correlation coefficient (r2) of 0.9994. The limit of detection (3[sigma]) and limit of quantitation (10[sigma]) were 0.021 [mu]g mL-1 and 0.081 [mu]g mL-1, respectively with a sample throughput of 40 h-1.