The external characteristics of the Mekong giant catfish were significantly as followed : 1. Eyes of every specimens situated below the mouth corner level, 2. The fin count were DII, 7; P1I, 10, P2I, 8: AIiv, 29-32; C, 17.,3. Caudal fin was lunate type and adipose fin was small size. The anatomical systems and organs of each system which seen in Mekong giant catfishes were revealed in this study as followed : 1. Integumentary - body covered by skin, no scale., 2. Digestive - found at terminal mouth, mouth cavity and pharynx, esophagus, stomach, intestine, liver, gall bladder and swim bladder., 3. Respiratory - found at nasal sac and gill., 4. Excretory - found at gill and both parts of kidney., 5. Reproduction - found at ovary and testis., 6. Circulatory - found at arterial circulation, venous circulation, heart and spleen., 7. Skeletal - found at cranium, vertebrae column, girdle and fin., 8. Muscular - found at body muscles, head muscles, fin muscles, eye muscles and branchial muscles., 9. Nervous - found at central nervous system, peripheral nervous system and autonomic nervous system., 10. Endocrine - found at pituitary gland, pineal organ and gonad.