Phytoremediation is an effective and low cost technology to remove different pollutants such as dye containing effluents from the environment. In the present study, the potential of Nasturtium officinale for degradation of C.I. Basic Red 46 (BR46) were investigated. The results revealed the decolorization ability of the plant species up to 87%. The metabolic fate of the dye was proposed by identification of six intermediate compounds produced during this process by GC-MS technique. Some physiological responses of the plant were evaluated under 10 and 20 mg/L of the dye with notable increase in superoxide dismutase, peroxidase and catalase activities as well as photosynthetic pigments content at high concentration. The results suggested induction of oxidative stress under dye treatment and demonstrated watercress's capacity to upregulate its antioxidative defense. The effect of some operational parameters (initial dye concentration, temperature, pH and amount of plant) on the efficiency of biological decolorization process was determined. The effect of initial BR46 concentration was more significant on dye removal efficiency. An artificial neural network (ANN) model was developed to predict the biodegradation efficiency. The results indicated that ANN provided reasonable predictive performance (R-2=0.965). (c) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.