Abstract: The changes of nitrogenous compounds (protein, nicotine and chlorophyll) in burley tobacco leaves during air-curing under 3 different barn humidities controlled artificially were studied. The results showed that: 1) the change of protein content mostly occurred during the early stages (wilting and yellowing stages) of air-curing particularly apparent in upper and middle leaves; the protein content tended to decrease during wilting stage under high or low barn humidities, the descending of protein content under middle barn humidity was more obvious and the tendency extended from wilting to yellowing stages; 2) the nicotine content in upper and middle leaves tended to increase during wilting stage under high or low barn humidities, the tendency continued during the yellowing stage under middle barn humidity; the change of nicotine content in lower leaf was slower than that in upper and middle leaves, and the nicotine contents in all leaves decreased slightly at later stage of air-curing; 3) the contents of chlorophyll in upper and middle leaves reduced obviously during wilting stage in the barns with high or low humidities, while the changes of chlorophyll content in upper and middle leaves had an obvious descending tendency both in wilting and yellowing stages under middle barn humidity; the chlorophyll content in lower leaf was less and changed little during air-curing.