A solid state fermentation was developed for citric acid production from pineapple waste by Aspergillus niger KS-7. The medium was supplemented with different concentration of glucose, sucrose, ammonium nitrate and ammonium phosphate. It was found that pineapple waste with 15% (w/v) sucrose and ammonium nitrate (0.25% w/v) gave the optimum citric acid secretion (60.61 g/kg) in the presence of methanol (2% v/v) when fermented for 5 days at 30 °C with the initial moisture content of 65%. The yield was more than 90% based on the amount of fermentable sugar consumed. These results present the use of pineapple peel as a cheap medium for the production of commercially valuable organic acid by A. niger.