A number of chemicals including carbon black, chitosan, benzalkonium chloride, sodium dodecyl sulfate, cyclodextrin, and zeolite13x were tested as odor-reducing fillers. The rationale is based on the concept of using odor absorbents/adsorbents for which both physical adsorption and chemical adsorption play an important role in odor reduction. The fillers were incorporated into highly odorous natural rubber (STR20 and RSS5) by physical mixing prior to sulfur vulcanization. As identified by gas chromatography and gas chromatography/mass spectrometry, the unpleasant odor mainly originates from low molecular weight volatile fatty acids. The quantity of acetic acid, a representative of odor molecule, can be significantly reduced in the presence of chitosan and zeolite13x. Although carbon black and cyclodextrin exhibited a tendency to reduce the odor, they were not as effective as zeolite13x and chitosan. On the other hand, commercial surfactants such as benzalkonium chloride and sodium dodecyl sulfate cannot serve as odor-reducing substances because of their limited thermal stability. An olfactometry test confirmed that chitosan and carbon black are good odor-reducing agents. Chitosan and carbon black showed a reinforcing effect on vulcanized rubber, whereas the surfactant deteriorated the strength of the rubber composite. (C) 2004 Wiley Periodicals, Inc.