In order to eliminate the inhibition effect of the toxic nitric oxide (NO) in flue gas on microalgal growth and CO₂ fixation, NO was converted by a wet UV/H₂O₂ method to produce nitrate (NO₃⁻), which then be used as a nitrogen source for microalgae to improve its growth. The growth ability and biomass compositions of the microalgae cultivated with the produced NO₃⁻ from NO gas were similar to those of the microalgae cultivated with equivalent moles of commercial NaNO₃. The NO₃⁻ concentration produced from NO increased with UV lamp power, H₂O₂, and NO concentrations, resulting in an improved microalgal growth. The concentration of NO₃⁻ from 500 ppm NO wet-oxidized by 6% (v/v) H₂O₂ and 55 W UV light was up to 8.8 mM. When the produced nitrate was used as supplementary nitrogen source, the maximum growth productivity of Chlorella PY-ZU1 at 15% (v/v) CO₂ reached 1.18 g L⁻¹ per day (0.97 times higher than that cultivated with the standard medium). The peak fixation efficiency of 15% (v/v) CO₂ was 69.6% (1.13 times higher than that cultivated with the standard medium).