Abstract: In order to study the variations of free amino acids in cut tobacco during primary processing, online sampling was conducted during SIROX heating and humidifying process and cylinder drying process. The amino acid contents (mass fraction) in three batches of nine cut tobacco samples were determined. Variations of free amino acids in cut tobacco from three process points were compared. The results showed that the contents and constitution of amino acids in cut tobacco changed significantly after processing. The analysis of variance indicated that the contents of alanine, glycine, valine, leucine, serine and threonine increased from 3.9% to 8.3% after SIROX heating and humidifying. On the other hand, the contents of valine, leucine, serine, phenylalanine and glutamic acid in cut tobacco significantly (P < 0.05) decreased from 1.7% to 3.0%. Principal component analysis suggested that based on the distribution of free amino acids in the nine samples, the cut tobacco from the same process point could be grouped into one category and their properties were well distinguished.