Sim established the electrical and household appliance company Osim International in 1979. After close to a decade, Osim branched out its operations into Hong Kong, and subsequently the Republic of China. Apart from Osim, Sim also owns the China-based Richlife, GNC in Southeast Asia, and the United States-based Brookstone. In 2012, he was listed as thirty-third on Forbes' "Singapore's 50 Richest" list. The following year, he rose to twenty-first. His estimated net worth increased to a billion dollars, mostly due to Osim's shares rapidly soaring.