The enforcement and evaluation of the inquiry experiment in the comprehensive experiments of water treatment for environmental engineering undergraduates are presented in this paper.In the course the students select a problem,and then design and conduct the experiment to address it.The students' experimental topics cover wastewater treatment,wastewater reuse and water environment rehabilitation.Each student is required to finish a questionnaire after completing the experiment.A statistical analysis of the completed questionnaire is made in order to compare the traditional experiment with the inquiry ones in improving the learning,and to evaluate the effectiveness of the inquiry experiment.Results from the survey show that the students appreciate the inquiry-based experiments,and believe that the experiments contribute to their understanding of basic and applied environmental concepts.Neither group size nor selection criteria has an influence on the performances of students within their groups.