The story of the coffee chain began when Loi Ah Koon emigrated from Hainan to Singapore and started a coffee, crackers, and toast shop at Telok Ayer Basin with two other people, but then the two partners stopped and let him run it alone. After getting married, his wife suggested cutting the bread into slices, baking it and combining it with her homemade kaya, which become their signature kaya toast.

Registered in 1944 as Ya Kun Coffeestall (Ya Kun being Ah Koon in Hanyu Pinyin), the stall gradually developed a reputation for delicious kaya toast and friendly service. As the children grew up, they began to help stir the kaya, run errands, charcoal-grill the bread and eventually, manage the stall.

After many store relocations, 1998 the stall moved to Far East Square and was renamed Ya Kun Kaya Toast. The following year, Ah Koon died and his youngest son, Loi Boon Sim Adrin took over the business, determined to “continue his father’s legacy”. Adrin decided to expand the business, opened a second store in Tanjong Pagar and in 2000, started franchising.

In 2002, the first overseas store opened in Indonesia and expanded its menu (adding ice cream toast and the Toastwich). In 2004 and 2005, the store won the Super Brand Award, the SIFST Product Award from 2005 to 2007, and the SPBA-CitiBusiness Regional Brand Award in 2008.

Ya Kun Kaya Toast has over forty Singaporean outlets, about half of which are franchised, and over thirty overseas outlets, all franchised, across seven countries (China, Indonesia, Japan, Myanmar, South Korea, Taiwan, Philippines, and the United Arab Emirates).

The stores have a retro ambiance, with wooden tables and stools, Chinese calligraphy of the company name, posters about their history, and traditional methods of preparing food and customer service reflecting Chinese family values. 

Unlike their main competitors, they have a limited menu that revolves around their core product, kaya toast, with cheese, peanut butter and ice cream as alternative spreads for their thin, brown, crispy bread. To appeal to a wider demographic, Ya Kun also sells French toast and Toastwiches (their Asian alternative to sandwiches).

According to Wikipedia