Abstract: Fourier transform infrared spectroscopy was applied to the determination of carbonate in an algae culture. Artificial neural networks was used to solve the severe influence of pH on the infrared spectra in the characteristic region. The predicted standard errors of NaHCO3 and pH value in the standard samples are 0.08 g/L and 0. 12, respectively. The results are better than that using partial least square method. This method has been proved to be an effective way to quantify the carbonate and pH value in an algae culture process.