Acipenser dabryanus lives only in the Yangtze River and Chin-sha River, and its natural populations have been damaged severely by long-term over-exploitation and increasing pollution. In 1988, the fish was listed as class Ⅰ state protected animal. It is immediately required to develop conservation measures for its populations, which requires both management and understanding of its biogeographical and biological chracteristics. Beacuase of the decline of natural spawning colony resource, there is litter knowledge about the sperm physio-ecological characteristics. Healthy male A.dabryanus individuals which had been cultured by our institute were selected and their spermatozoa were collected. The density of spermatozoa was determined by counting using a haemocytometer after 1 000× dilution of samples with 0.65% NaCl extender, and the results from three replicates were averaged. Milt concentration was enumerated by using milt collected into standard centrifuge tubes and centrifuged at 4 000 r/min for 30 min. The sperm cell volume percentage in the total volume of semen was calculated from 5 replicates. Semen pH was measured with a precision test paper. Ionic composition of seminal plasma was measured by the atomic absorption spectrophotometry method with the use of a AA_220 spectrometer (Varian USA). The effects of different aqueous solution on the sperm motility were measured by using different sources of test water, and Na , K sensitivity of sperm motility was assessed by activating sperm with 20, 40, 60, 80, 100, 120 mmol/L NaCL and 0.01, 0.05, 0.10, 0.50, 1.00, 1.50 mmol/L KCl, respectively. For testing the motility of spermatozoa, 1 μl of milt was mixed directly with 30 μl of the experimental solution, placed on a glass slide and examined under 400× magnification. The ultrastructure of spermatozoa was observed by using SEM (scanning electron microscopy) and TEM (transmission electron microscopy). All statistical analyses were conducted with SPSS STATISTICS, Version 17.0. For multiple comparisons between groups with LSD method, statistical significance was declared at P < 0.05. Results were presented as mean ± standard deviation (SD). The results showed that the sperm density of A.dabryanus was 0.63 × 109 to 2.73 × 109/ml, with the average of 1.52 × 109/ml, the concentration of sperm was 3.18% to 12.98%, with the average of 7.67%, and the pH value was between 7.5 and 7.9 (Table 2). The ions composition in seminal plasma of A.dabryanus included Na , K , Ca2 , Mg2 , Cu2 , Zn2 , and Na was the main ion in seminal plasma, followed by K , Mg2 , Ca2 , Cu2 , Zn2 . There was significant difference in the concentration of Na , K , and Zn2 (P < 0.01), but no significant difference in Ca2 , Cu2 , Mg2 (Table 3). In A. dabryanus, the Na , K concentrations were lower than in teleostean fish (Table 4).The sperm had the highest motility in river water, and the fast movement time (FT) and lifetime (LT) were 142 s and 373 s, respectively (Fig. 1). The activity of A. dabryanus sperm in NaCl solution reached the highest when its concentration was 20 mmol/L, with the FT and LT being 66.7 ± 7.1 s and 177.0 ± 14.9 s, respectively (Fig. 2a). When the concentration of K was 0.05 mmol/L, the motility of sperm was the highest, while the FT and LT were the longest, which were 109.0 ± 16.1 s and 189.3 ± 12.4 s, respectively (Fig. 2b). The average length of the nucleus was 5.67 ± 0.20 μm (Table 5). Three intertwining endonuclear canals traversed the nucleus longitudinally from the acrosomal end to the basal nuclear fossa region. There were three mitochondria in the midpiece. The flagellum (63.16 ± 2.79 μm in length), originating from the centriolar apparatus, had a typical 9 2 eukaryotic flagellar organization (PlateⅠ). Some A. dabryanus sperm characteristics are reported here, but further investigations are needed in order to improve our knowledge of reproductive biology of this species and to establish gamete management methods.