Algal allelopathy is an ecological or physiological phenomenon that has focused attention on the interactions among algae and the production of algal toxins. A species of marine bloom-forming microalga: Amphidinium carterae was selected in the present study to estimate its potentially allelopathic effects on other species of microalgae. The cell-free filtrates of A. carterae in two growth phases: exponential grwoth phase (abbreviated as growth phase Ⅰ) and stationary growth phase (abbreviated as growth phase Ⅱ) were prepared, and its inhibitory effects on growth of other species of marine microalgae were studied under stable environmental conditions (temperature, light and illuminating periodicity, etc.). The cell-free culture filtrates were prepared firstly when A. carterae were cultured phaseⅠand phaseⅡ, which was about the the growth 7^th and 17^th respectively, and enriched with f/2 medium. The above prepared culture filtrates were used to culture 4 species of marine microalgae: Skeletonema costatum、Prorocentrum micans、Scrippsiella trochoidea and Isochrysis golbana. Moreover, the crude extractions in the cell-free filtrate of A. carterae of growth phaseⅡ were extracted by GC/MS, and the major components were analyzed. Results showed that: in the enriched cell-free filtrates, S. costatum were obviously inhibited in either filtrates of phase I (F=15.18475, P=0.00298<0.05) or phase Ⅱ(F=6.24559, P=0.03149<0.05) as compared to that in the control which in f/2 enriched medium, but the cell numbers of S. trochoidea were only about 79.3% and 68.9% in filtrates prepared from phaseⅠand phaseⅡ as compared to the control by the end of experiment. As to P. micans, its growth was obviously suppressed (F=4.84438, P=0.04925<0.05) in the filtrate prepared from phaseⅡduring the last 3 days. Little inhibition was observed in I. golbana in either filtrates prepared from either phases (P>0.05). Cell-free filtrate cultures experiment of A. carterae is one of the basic approaches on allelopathy research. Results in the present study suggested that A. carterae secreted or released some substances into the culture medium, which inhibited the co-cultured S. costatum and P. micans, and these inhibitory effects could not caused by light, nutrients or cell contact to gain a competitive advantage. Many algae could release allelochemicals into the environment which may alter phytoplankton growth to enhance its predominance. Besides, growth of these two species was more inhibited in enriched cell-free filtrate prespred from growth phaseⅡ than that from phaseⅠ. It also proved that the allelochemical effects on algae were species-specific because growth of S. costatum and P. micans was inhibited, but exerted little effects on S. trochoidea and I. golbana. Another experiment was performed to further prove the allelopathic effect of A. carterae.The crude extractions from cell-free filtrates of A. carterae at different concentrations were added into S. costatum and P.micans culture media, found that cells dissolved in higher concentration after many hours. It is noted that the crude extractions had the function of dissolving some algal cells. Then the crude extractions were analyzed by GC/MS. Four components in the crude exactions were suspected to have the allelopathic effects, they were Butylated Hydroxytoluene, Butyl citrate, Benzene, 1-Chlorodifluoromethoxy-4-nitro-, and Benzyl butyl phthalate, among with Butylated Hydroxytoluene (BHT) was reported with oxidative characteristic and was used as an antioxidant additive. Results in the present study brought light on the hypothesis that A. carterae could realese allelochemical(s); however, deep research should carry out to explain the possible inhibiting mechanism.