Abstract: In order to determine the protein nitrogen in tobacco fast, the non-protein nitrogen in soluble nitrogen was extracted from tobacco sample with heated 0.5% acetic acid, in which soluble proteins in tobacco precipitated, and then determined with a continuous flow analyser.The protein nitrogen content in tobacco was figured out by subtracting the determined non-protein nitrogen from total nitrogen.The results showed that the CV of the method was less than 3%.There was no significant difference between the values determined by this method and current industry standard method at the confidence interval of 90%.