Abstract: To treat Pinellia processing wastewater, the toxicity on activated sludge was evaluated in this study. The raw Pinellia processing wastewater and the wastewater after treated by flocculation was investigated comparably by establishing the degradability of wastewaters, the oxygen uptake rate (OUR), dehydrogenase activity (DHA) and microbial survival. Results indicate that Pinellia processing wastewater inhibits the activity of activated sludge, even leading to lethal effects on bacteria. The semi-inhibitory volume fraction based on DHA and OUR evaluation is 74% and 60%, respectively. The semi-lethal volume fraction is 61.38%. The degradability of this wastewater is dependent on the toxicity concentration. DHA and OUR is highly related to the lethal volume fraction, suggesting that the lethal effect of Pinellia processing wastewater results in the decrease of degradability of this wastewaters. However, the flocculation treatment is established as one solution of detoxification on microbes. After the flocculation treatment, the biodegradability of Pinellia processing wastewater is improved due to the weakened toxicity of the wastewater.