The lysine price-fixing conspiracy was an organized effort during the mid-1990s to raise the price of the animal feed additive lysine. It involved five companies that had commercialized high-tech fermentation technologies, including American company Archer Daniels Midland (ADM), Japanese companies Ajinomoto and Kyowa Hakko Kogyo, and Korean companies Sewon America Inc. and Cheil Jedang Ltd. A criminal investigation resulted in fines and three-year prison sentences for three executives of ADM who colluded with the other companies to fix prices. The foreign companies settled with the United States Department of Justice Antitrust Division in September through December 1996. Each firm and four executives from the Asian firms pleaded guilty as part of a plea bargain to aid in further investigation against ADM. The cartel had been able to raise lysine prices 70% within their first nine months of cooperation.

The investigation yielded $105 million in criminal fines, a record antitrust penalty at the time, including a $70 million fine against ADM. ADM was fined an additional $30 million for its participation in a separate conspiracy in the citric acid market and paid a total fine of $100 million. Three former high-ranking ADM executives were convicted in September 1998 after a ten-week jury trial. Buyers of lysine in the United States and Canada sued and recovered $80 to $100 million in damages from the five cartel members, and ADM paid $38 million to settle mismanagement suits by its shareholders.

The lysine cartel was the first successful prosecution of an international cartel by the U.S. Department of Justice (DOJ) in more than 40 years. Since then, the DOJ has discovered and successfully prosecuted nearly 20 international cartels.