The objective of this study was to characterize the morphological and anatomical properties by double-dyeing with carmin vert d'iode, determine chromosome number of root tip by using hypo-osmotic shock method, detect qualitatively phytochemical compositions and assess the antibacteria against E. coli and B. subtilis of leaf and tuber extraction of Colocasia gigantea. The results showed morphological characters and microscope transverse sections of fresh leaf, tuber and root of C. gigantea. The chromosome number at root tip was 2n = 28. The preliminary phytochemical components were detected at leaf extract as steroid, flavonoid, alkaloid, tannin, glycoside and coumarine. At tuber, the chemical components were the same except alkaloid. Saponin was absent in both leaf and tuber extract. The antimicrobial activity against E. coli and B. subtilis was showed that leaf and tuber methanol extraction of C. gigantea inhibited the growth of both bacteria at 200 mg/ml, 400 mg/ml and 800 mg/ml) (p At both leaf and tuber extraction, the diameter of inhibition zone against B. subtilis was statiscally different from that of E. coli (p . C. gigantea is used as a food ingredient and traditional medicine.