The results revealed that essential oil concentration in microparticles had the most important influence on the diameter of the inhibition zone against tested mic- roorganisms, as well on the diameter of chitosan mic- roparticles that were made. The increase of the con- centration of thyme essential oil in the chitosan micro- particles induced an increase in the diameter of the inhibition zones of the tested microorganisms. On the other hand, the diameter of chitosan micropaticles decreased with increasing the concentration of the cross-linking agent glutaraldehyde, that was used for preparing microparticles. It is important to emphasize