In order to suppress the growth of Chroococcus turgidus and finally eliminate it during the amplification process of filaments of Scytosiphon lomentaria, the effects of four antibiotics:cefotaxime sodium (CTX), amoxicillin (AM), tetracycline (TC) and erythromycin (EM) on the growth of filaments of S. lomentaria and C. turgidus, which were co-cultured in the research, were studied by experimental ecology methods in this paper. Results indicated that CTX can inhibit the growth of C. turgidus significantly at the concentration of 50 and 100 mg/L. On the 20^th day, their average daily growth rates were 3.84% and -0.96%, respectively, which were significantly lower than 19.21% in the control group without antibiotics, therefore ensuring the normal growth and development of filaments of S. lomentaria. Both C. turgidus and the filaments of S. lomentaria were not suppressed by AM at the concentrations between 50 and 1 000 mg/L, so AM can not eliminate C. turgidus in the co-culture system. TC could inhibit the growth of C. turgidus and the filaments of S. lomentaria dramatically at the concentration of 100 and 200 mg/L, but the cytoplasm of filaments of S. lomentaria presented atrophy. EM inhibited the growth of C. turgidus significantly at the concentrations between 0.10 mg/L and 1.00 mg/L, when the concentration was higher than 0.50 mg/L, the growth of filaments of S. lomentaria also were inhibited, even to death.