The present work reveals the preliminary phytochemical screening and the study of antimicrobial activities of Costus speciosus (Koen) and Sea Qust. These are medicinal plants of considerable importance. Carbohydrates, Tannins, Steroids, Anthocyanates and Proteins were detected in both plants. Alkaloids, saponines, Anthraquinones were present in Costus speciosus but where absent in Sea Qust. The antibacterial and antifungal activity of essential oils and plant extracts of Costus Speciosus and Sea Qust was investigated against a few pathogens viz. M. gypseum, M. canis, C. albicans and C. tropicalis, P. aeruginosa and S. aureus, P. aeruginosa and St. aureus. The data obtained validated their wide application for therapeutic purposes in alternative therapy.