The companies face a penalty of 44.6bn won ($39m; Â£25.2m), said the Fair Trade Commission (FTC).
The regulator said the two firms held secret meetings in 2008 and 2009 to agree on prices for washing machines, flat-panel TVs and laptop computers.
Samsung and LG are the largest makers of the products in South Korea.
"Their price rigging caused damage to many consumers by leading the prices of washing machines, flat-panel TVs and laptop computers to rise more than other competing products," the FTC said.
Samsung was fined 25.8bn won, while LG was fined 18.8bn won.
South Korea's antitrust regulator has fined Samsung Electronics and LG Electronics for conspiring to fix the prices of some appliances.