In order to evaluate growth, yield, photosynthesis and antioxidant activity of chilli under interactive application of potassium (K) and wastewater (WW). Five different doses of K at the rate of 0, 25, 50, 75 and 100kgha−1 were given along with a uniform dose of nitrogen (N) and phosphorus (P). The growth and biochemical parameters were studied at 60days after transplantation (DAT), while yield and antioxidant contents were estimated at harvest. Evaluation of data revealed that K50 proved optimum for all parameters studied but in combination with 100%WW it proved more effective. In addition K100 was excessive, while, K25 was deficient. However, deficient dose with 100%WW also proved economical as it was at par with GW×K50 for most of the parameters studied, showing the utility of the WW as a source of nutrients. Thus,WW has an important role in nutrient supplementation and also growth and yield of crop plants.