Randomly selected essential oils and some terpene and phenolic derivatives were evaluated for their ability to modulate human cellular immune responses using various inflammatory parameters including reactive oxygen species (ROS) generation from whole blood phagocytes and isolated polymorphonuclear neutrophils (PMNs), proliferation of T-cells, IL-2. and TNF-α cytokine production. The essential oils from Foeniculum vulgare, Saturea cuneifolia, and Origanum munitiflorum inhibited ROS produced from whole blood phagocytes, while thymol, carvacrol, rosmarinic acid, caffeic acid, quercetin, and kaempferol glycoside potently inhibited the ROS production from whole blood as well as from isolated PMNs, among which caffeic acid, quercetin, and kaempferol glycoside exhibited a better inhibitory effect than that of ibuprofen. The compounds rosmarinic acid, caffeic acid, quercetin, kaempferol glycoside, genistein, and apigenin (IC50 7.0±0.5, <3.12, <3.12, 4.3±1.0, 5.8±0.5, and <3.12μg/mL) were found to exert potent inhibition on proliferation of T-cells. On the other hand, quercetin (IC50 2.9±0.3μg/mL) and apigenin (IC50 <1.0μg/mL), were also found to be the potent inhibitor of IL-2 cytokine. The essential oils of Mentha species, and compounds quercetin and apigenin were found to potently inhibit the production of pro-inflammatory cytokine TNF-α. The results indicated that essential oils and phenolics might be considered as promising immunomodulatory agents.