Abstract: Nitrate and nitrite react with 2,6-xylenol in H₂SO₄solution. On the basis of this fact we simutaneously determined nitrate and nitrite with dual-wavelength at 318nm-290.5nm and 305.5nm-332.5nm. Beer's law is obeyed in the range 0.00-19.03μg NO₃^--N/25ml and 0.00-12. 00μg NO₂^--N/25ml and △ε_318;390.5nm is 2.3×10³and △ε_305,332.5nm is 4.74×10³. After neutralization of solution with NaOH, spectra took place bathochromic shift and nitrate and nitrite can be determined with dual-wavelength at 417.5nm-359nm and 384nm-463.5nm. Beer's law is obeyed in the range 0.00-7.61μg NO₃^--N/25ml and 0.00-4.8μg NO₃^--N/25ml and △ε_417.5,359nm is 1.13×10⁴and △ε_384,463.5nm is 1.29×10⁴This methed was applied to determine of nitrate and nitrite in water.