The effect of Spirulina platens is and probiotics as feed additives on the growth of the shrimp Fenneropenaeus chinensis was investigated in comparison with a control. The shrimp were cultured in rearing tanks in a seawater pond for 35 days from September 1, 2004. As regards the water quality, the probiotic treatment (T2, commercial diet and 3% probiotics) produced a lower TDN (total dissolved nitrogen) and TDP (total dissolved phosphorus), making it effective in water quality improvement. Nonetheless, the phytoplankton flora succeeded from diatoms to cyanobacteria, regardless of the feed additives. Treatment T3, including 3% S. platensis, produced the highest mean body weight, which was 39% higher than that for all the other treatments (P<0.05). Accordingly, it was found that the use of Spirulina and probiotics as feed additives increased the shrimp body weight and improved the water quality, respectively.