The utility of the juice of rotten or discarded pineapples and the waste material of the production of pineapple juice as low-cost substrates for ethanol production by Zymomonas mobilis was investigated. Z. mobilis ATCC 10988 produced 59.0 g.l(-1) ethanol in undiluted pineapple juice without nutritional supplementation and without the regulation of the pH while 42.5 g.l(-1) ethanol was obtained using a 125 g.l(-1) sucrose medium supplemented with 10 g.l(-1) yeast extract and mineral salts. Ethanol fermentation using unhydrolyzed and enzymatically hydrolyzed pineapple waste material was also investigated under various culture conditions. When a 15% (v/v) dilution of unhydrolyzed waste material without nutritional supplementation was used, more than 3.5 g.l(-1) ethanol was produced. When the media containing 15, 30, and 40% (v/v) of the hydrolyzate consisting of a 60% (v/v) suspension of pineapple waste material were used, final concentrations of ethanol were 5.0 g.l(-1), 7.6 g.l(-1), and 9.3 g.l(-1), respectively. These results suggest that pineapple juice and the waste material can be useful low-cost substrates for ethanol production by Z. mobilis without supplementation with expensive organic nitrogen complexes such as yeast extract and without the regulation of the pH during cultivation, leading to the reduction in the production costs.