This study investigated the change of hazardous materials in coking wastewater at different treatment stages (anaerobic, anaerobic/aerobic, anaerobic/aerobic/photo degradation, anaerobic/aerobic/ozone oxidation treatment) and the effects of them on the development of maize embryos and the activity of amylase and protease in maize seeds. Moreover the interaction of refractory organic matters in the wastewater at different treatment stages with amylase and protease also were determined in vitro. The results show that the biodegradable and the refractory organic compounds in the wastewater both can affect maize embryo development (germination inhibition rate is 19.3% for biodegradable organic compounds). As the treatment stage preceding, the inhibition effect of coking wastewater on the development of the maize embryo (for germination inhibition rates change from 49.3% to 24.6%) and on enzymatic activity (inhibition rates change from 63.9% to 22.4% for amylase) decreases gradually, but the photodegradation treatment to anaerobic/aerobic effluent can increase its toxicity. The changes in the ability of the refractory organic compounds to bind with enzyme proteins, combined with the analysis of the organic components by GC/MS, show that in the process of coking wastewater treatment no new toxic chemicals were produced. (C) 2012 Elsevier B.V. All rights reserved.