Some of preliminary investigation results on morphological, sex organization and reproductional ecology of knifefishes at Thua Thien Hue province were revealed and modified follow age groups. In 1+ age group, this kind of fish is cannot be identified its sex. Knifefish's sex is nearly clarified at the approximately 1+ age group and the maturation in the first time at the 1+ age group. The papulas has distributed of ambilateral cloacal aperture are the feature of visual discrimination between the male and female of knifefishes on a morphology. At the same time, the morphology of knifefish's ovarium and sperm are the different with special features depend on growth stages. In general, the rate of female fish is more than male fish with 49,3 percent and 40,2 percent respectively. The coefficient of fat of Fulton is higher than that of Clark and will increase along to age of fish. The coefficient of fat of female fish (Fulton: 869.10-6, Clark: 795.10-6) is higher than that of male fish (Fulton: 701.10-6, Clark: 672.10-6). The spawning season of knifefish happens from March to June, in which fish have egg-laying overstock from May to June every year.