In order to investigate the effects of dissolved oxygen level on the fast-start performance of juvenile grass carp (Ctenopharyngodon idellus), this paper studied the faststart process of hypoxiaacclimated (1 mg O₂·L^-1, 48 h) and nonacclimated C. idellus juveniles in normoxia (c. 10.0 mg O₂·L^-1), 2.0 mg O₂·L^-1, and 1.0 mg O₂·L-¹ at 15.0±1.0 ℃. The juveniles were electrically stimulated (0.75 V·cm^-1, 50 ms), their faststart process was recorded by high speed camera, and their responsiveness (R), response latency (T), maximum swimming speed (V_max), maximum acceleration (A_max), 160 ms cumulative distance (S), and curvature coefficient (C) were calculated. As compared with those in normoxia, the R of nonacclimated juveniles in hypoxia decreased, while the V_max, A_max, and T increased. Dissolved oxygen level had no significant effects on the S or C. Hypoxia acclimation only induced the increase of the T, but had no significant effects on the other measured parameters. It was suggested that hypoxia acclimation and the decrease of dissolved oxygen level could induce the decrease of R and the increase of T, while the increased T in hypoxia could be due to the decreased sensitivity of nervous system in hypoxia. Both the hypoxia acclimation and the dissolved oxygen level showed no significant effects on the faststart performance of the juvenile C. idellus, indicating that the rapid escape performance of the juvenile C. idellus in hypoxic environment was relatively conservative.