Abstract: Acetaldehyde wastewater contains high concentration of toxic organic compounds, including aldehydes and organochlorines. It has strong inhibition on the microorganisms in wastewater biological treatment system, and it is difficult to treat directly by biological treatment, so detoxification pretreatment is needed. The effects of prolonging reaction time and raising reaction temperature on the dosage of alkali required for alkaline detoxification of acetaldehyde wastewater were investigated. The results indicated that alkaline pretreatment could effectively remove aldehydes and organochlorine toxic organic compounds from wastewater, and significantly reduce the anaerobic biological toxicity and aerobic biological toxicity of wastewater. The anaerobic biological toxicity was more reasonable for the evaluation of detoxification efficiency than the concentration of toxic substances. Prolonging reaction time and raising reaction temperature were beneficial to reducing the alkali dosage required for sufficient detoxification of acetaldehyde wastewater. When the reaction time was prolonged from 3 h to 10 h, the reaction temperature was raised from 60 ℃ to 70 ℃, the alkali dosage required for the sufficient detoxification was reduced by 50%, and the cost of regents saved by about 3.7 yuan per ton of wastewater.