This study dealt with the in vitro camparison of the comparison of the antiplatelet aggregration activity of the fresh leaves of Andropogon citratus Linn. (lemon grass) and Mentha arvensis Linn. (yerba buena on human) platelet aggregration. Lemon grass and yerba buena were chosen on the basis of their reported benefacial effects on cardiovascular diseases (CVD). Patients with CVD have high risk of thrombosis and this where antiplatelet therapy does it role. Fresh leaves of lemon grass and of yerba buena were by maceration and solvent-partitioning method using the three solvents; hexane, ethyl acetate and ethyl alcohol. The four test solutions of each plant were the (1) crude alcohol extracts, (2) hexane-free extracts, (3) ethyl-acetate free extracts and (4) ethanol-free extracts and different concentrations(4 mg/mL, 10 mg/mL, 100 mg/mL, 250 mg/mL and 500 mg/mL)were prepared for each test solution. These were compared to the positive control, Aspirin USP(10 mg/mL) and the negative control, normal saline solution (NSS). To induce platelets in suspension to aggregrate, 025M Calcium chloride was used. Giemsa dye was used to visualize platelet aggregration in the form of violet-colored gels. Antiplatelet aggregrations activity was tested using Giemsa Microplate Assay(Pimentel etal. 2002). Results showed that both lemon grass and yerba buena have antiplatelet aggregration activity at higher concentrations.The test solutions yield negative activity on lower concentration as shown by the presence of violet-colored gels int microplate .Isolation and identification of the active constituents of the plant that are responsible for the antiplatelet for aggregration activity may be conducted through tests such as Thin Layer Chromatography(TLC) and Gas Chromatography-Mass Spectroscopy(GC-MS). Formulation into dosage forms such as capsules ora as tea is also recommended.