Abstract: In this paper, the Myanmar indigenous medicinal plant, Couroupita Guianensis Aubl. (Amyauk-San-Bin), was studied. The phytochemical constituents of C. Guianensis was investigated and the antimicrobial activities of n-hexane, dichloromethane, ethyl acetate, ethanol and methanol extracts of C. Guianensis was tested by Agar-well diffusion method on six selected organisms Bacillus subtilis, Staphylococcus aureus, Pseudomonos aeruginosa, Bacillus pumilus, Candida albican and E-coli.