ONE 166

ONE 166: Qatar was a combat sport event produced by ONE Championship that took place on March 1, 2024, at Lusail Sports Arena in Lusail, Qatar.

Background
This event marked the organization's debut in Qatar. It also the second visit to Middle East, since ONE FC: Reign of Champions in Dubai, United Arab Emirates in August 2014.

A ONE Middleweight World Championship bout between current champion Reinier de Ridder (also former ONE Light Heavyweight World Champion) and the ONE Light Heavyweight and Heavyweight Champion Anatoly Malykhin headlined the event. The pairing previously met at ONE on Prime Video 5 in a light heavyweight title, which Malykhin captured the title by first round knockout. If successful, Malykhin would become the first fighter in MMA history to win championships in three divisions as well as to hold them simultaneously.

A ONE Featherweight World Championship unification rematch between current champion Tang Kai and former champion/current interim title holder Thanh Le took place at the co-main event. The pairing previously met at ONE 160 which Tang captured the title by unanimous decision. The pairing was previously scheduled to meet at ONE Fight Night 12, but Tang withdraw from the bout due to a knee injury.

A ONE Strawweight World Championship rematch between current champion Jarred Brooks and former two-time champion Joshua Pacio took place at the event. The pairing previously met at ONE 164, where Brooks captured the title by unanimous decision.

A ONE Women's Atomweight World Championship bout between current champion Stamp Fairtex (also ONE Women's Atomweight World Grand Prix winner, former ONE Women's Atomweight Muay Thai and Kickboxing World Champion) and Denice Zamboanga was expected to take place at the event. However, the bout was moved to June so the fighters can take part in the start of an original docuseries production.

A ONE Welterweight Submission Grappling World Championship bout between current champion Tye Ruotolo and Izaak Michell was expected to take place at the event. However, the bout was moved back to April for unknown reasons.

Former ONE Bantamweight Muay Thai World Champion Nong-O Hama was expected to face Vladimir Kuzmin in a bantamweight Muay Thai bout. However, Nong-O was removed from the bout for unknown reason and was replaced by promotional newcomer Zafer Sayik in a catchweight of 147.75 pounds.

Bonus awards
The following fighters received $50,000 bonuses.
 * Performance of the Night: Anatoly Malykhin and Tang Kai