Objective:To investigate the effects of 20 methanolic extracts from Malaysian selected plants on CD18/11 a expression and phagocytosis activity of leukocytes using flow cytometry analysis.Methods:The effects of methanolic extracts on CD18/11 a expression and phagocytosis of leukocytes were measured by labelling the cells with CD18-fluorescein isolhiocyanaie and ingestion labelled with Escherichia coli-fluorescein isothiocyanate and then analyzed using flow cytometer.Results:About 12 out of 20 methanolic extracts of selected Malaysian medicinal plants significantly(P≤0.05) inhibited the CD18/1 la expression of leukocytes at both concentrations of 6.25 μg/mL and 100 μg/mL in dose dependent manner.The most active inhibitory was shown in Citrus aurantifolia(Christm.) Swingle and Alpinia galangal(L.) Willd.at dosage 100ug/mL.Moreover,the Orthosiphon aristatus(Blume) Miq(O.aristatus).showed the highest stimulatory activity at the concentration of 100 μg/mL.Other than that,four plant extracts significantly(P<0.05) rose the phagocytosis activities of leukocytes in dose dependent manner.However,Annona muricata L.and O.aristatus showed the highest stimulated activities at the 100 pg/mL concentration.Conclusions:The results suggest that methanolic extracts of Cirrus aurantifolia.Alpinia gaiangal,O.aristatus and Annona muricata are able to modulate innate immune system and can potentially be recognized as therapeutic agents for modulating immune system. Objective: To investigate the effects of 20 methanolic extracts from Malaysian selected plants on CD18 / 11 a expression and phagocytosis activity of leukocytes using flow cytometry analysis. Methods: The effects of methanolic extracts on CD18 / 11 a expression and phagocytosis of leukocytes were measured by Results: About 12 out of 20 methanolic extracts of selected Malaysian medicinal plants significantly (P ≦ 0.05) inhibited the CD18 / 1 la expression of leukocytes at both concentrations of 6.25 μg / mL and 100 μg / mL in dose dependent manner. The most active inhibitory was shown in Citrus aurantifolia (Christm.) Swingle and Alpinia galangal (L.) Willd. at dosage 100 ug / mL. Moreover, the Orthosiphon aristatus (Blume) Miq (O. aristatus). Showed the highest stimulatory activity at the concentration of 100 μg / mL. Of that than four plants ext racts significantly (P <0.05) rose the phagocytosis activities of leukocytes in a dose dependent manner. However, Annona muricata L. and O. aristatus showed the highest stimulated activities at the 100 pg / mL concentration. Conclusions: The results suggest that methanolic extracts of Cirrus aurantifolia. Alpinia gaiangal, O.aristatus and Annona muricata are able to modulate innate immune system and can potentially be recognized as therapeutic agents for modulating immune system.