A fuzzy logic model was constructed to predict hydraulic jump aeration efficiency. Fuzzy subsets and rules were created based on experimental observations and measurements carried out in a 0.5m wide flume with upstream Froude and Reynolds numbers of 2.3-6.4 and 1.4-5.4 x 10(4), respectively. A strong correlation was found between the aeration efficiency and Froude number. Upstream Froude and Reynolds numbers were selected as input parameters for the model. In this study, rather than mathematical equations, linguistic expressions were used to relate the upstream Froude and Reynolds numbers with aeration efficiency in an IF-THEN format. The proposed fuzzy model made good predictions and captured the system dynamic behaviour. Experimental observations confirmed the fact that hydraulic jump can be used as an aerator and mixing device in water treatment plants. Estimation of the aeration efficiency of a hydraulic jump could be made by any designer with the help of the fuzzy logic procedure described in this paper.