Abstarct: A simple, low cost and sensitive method baxsed on solvent microextraction (SME) for separation/preconcentration coupled with flam atomic absorption spectrometry was proposed for the determination of trace amounts of cobalt (II). The analytical procedure involved the formation of a hydrophobic complex by mixing the analyte solution with an 2-Nitroso-1-naphtol(2NP) solution. The effect of affenent parameters such as pH, concentration of ligand, kind of buffer, kind and volume organic solvent, extraction time, stirring rate of sample solution, temperature and ionic strength were investigated. Also effects of foreign ions were stadied. In the suitable conditions, the complex of cobalt-2NP entred into micro organic phase and separation of analyte from the matrix was achieved. Under the optimized chemical and instrumental conditions a linear calibration curve in the range of 10-400 mg/L , with detection limit 0.20 mg/L and enrichment facror of 25/83 were achieved, respectively the relative standard deviation for six replicate determination of 80, 160 and 300 mg/L of cobalt were %2.18, %1.73 and %2.33, respectively.The metod was successfully applied for determination of cobalt (II) in the natural and spiked water samples.