Bio-diesel is a mixture of fatty acid methyl esters, and is produced by trans-esterification of renewable feed-stock. This study develops an economically attractive and environmentally acceptable bio-diesel production process using multi-objective optimization. It considers bio-diesel production using waste cooking oil as the feed-stock, which can reduce bio-diesel cost. Both the pre-treatment and trans-esterification sections of this process are simulated in a process simulator followed by optimization for multiple objectives using multi-objective differential evolution with taboo list. Profit, fixed capital investment and organic waste from the biodiesel process are considered as objectives for optimization. Effect of variation in feed flow rate on process performance is also studied. The results show that the amount of organic waste can change significantly with only small variations in the economic objectives, and they provide alternative process designs with different environmental impacts, for implementation. (C) 2012 Elsevier Ltd. All rights reserved.