Among the metal hydrides, sodium borohydride has the advantages of high hydrogen storage capacity, controlled hydrogen gas evalution with a suitable catalyst, and possibility of recycling after hydrogen production. Quantitative analysis of sodium borohydride was studied using spectrophotometric method. The analysis was based on the reduction of the additive agent, phosphotungstate. On the calibration curve for sodium borohydride stock alkaline solution, deviations from the linearity was observed at both ends of the concentration interval. As the accuracy in correct prediction of the concentration of the unknown solutions was desirable in such calibration curves, a third order polynomial was fitted through all the points in the calibration curve. The deviation from the linearity may be attributed to the heteropoly blue species, which can be reoxidized by the oxygen present in the air to the colorless phosphotungstate form. When the sample gets oxygenated, the absorbance at 680 nm might decrease with time. Thus, it is very important to carry out the experiments quickly. This is an abstract of a paper presented at the 18th International Congress of Chemical and Process Engineering (Prague, Czech Republic 8/24-28/2008).