The story of Uni Air, formerly known as Mandarin Airlines, began in 1991 when China Airlines, the largest carrier in Taiwan, spun off its domestic routes. The Taiwanese government established the airline as a subsidiary of China Airlines, with the main purpose of competing with other domestic airlines in the country.

Uni Air's fleet was initially composed of Boeing 737-800 and ATR 72-500 aircrafts, but over the years, the fleet has grown to include other aircrafts such as the ATR 72-600 and the Airbus A321neo. As of 2021, the airline operates a fleet of 53 aircrafts, which include a mix of ATR 72-500, ATR 72-600, Boeing 737-800, and Airbus A321neo.

Throughout its history, Uni Air has had several important milestones. In 1998, the airline began offering international flights to Seoul, South Korea. This marked the first time that Uni Air had flown outside of Taiwan. In 2004, the airline became the first Taiwanese carrier to introduce the ATR 72-500 aircraft. This allowed the airline to expand its route network and offer more services to its customers.

In 2006, Uni Air became the first Taiwanese carrier to introduce the ATR 72-600 aircraft, which allowed the airline to expand its route network further and to offer more services to its customers. In 2010, the airline began offering flights to Palau and Guam, marking the first time it had flown to destinations outside of Asia.

In addition to these milestones, Uni Air has also faced some challenges over the years. In 2008, there was an incident involving one of Uni Air's ATR 72-500 aircrafts that caused the aircraft to be damaged beyond repair. However, no injuries were reported. In 2012, the airline was the subject of a federal investigation following allegations of price-fixing. The investigation was ultimately dropped.

Overall, Uni Air has come a long way since it was established in 1991. From its humble beginnings as a subsidiary of China Airlines, the airline has grown to become one of the leading carriers in Taiwan, offering international flights to destinations outside of Asia. Through its fleet of 53 aircrafts and its commitment to providing a high-quality experience to its customers, Uni Air continues to make significant strides in the aviation industry.