The Toyota Mark X (Japanese: トヨタ・マークX, Hepburn: Toyota Māku X) is a mid-size car manufactured by Toyota between 2004 and 2019, and was primarily aimed at the Japanese market. The Mark X was introduced in 2004 and is the successor to the Mark II which was first introduced in 1968, and was known in the North American market as the Corona Mark II starting in 1972, and renamed the Cressida from 1977 to 1992.

The "Mark X" is not pronounced "Mark Ten" but "Mark Ex", though the "Mark II" is "Mark Two". The Mark X is a continuation of the previous Mark II and its siblings, the sport-orientated Chaser, and the luxurious Cresta in one vehicle, repeating an approach previously attempted by the short-lived Verossa that used inline-six engines, whereas the Mark X uses V6 engines.

The Mark X was previously sold as an alternative to the front-wheel drive Camry, which was once the largest new saloon at Corolla Store locations, for buyers who like the size of the Camry, but prefer a rear-wheel drive layout.

Different engine sizes were offered to allow Japanese buyers to choose which annual road tax they were willing to pay; the larger engines offer higher levels of standard equipment and luxury features. Both the first and second generation Mark X were manufactured at the Motomachi plant in Japan.

The Mark X was sold as the Reiz (Chinese: 锐志; pinyin: Ruìzhì) in China, which was produced by Tianjin FAW Toyota Motor Co. Ltd. It was produced until 2017. The Mark X was also officially imported to Indonesia in limited quantities between 2012 and 2013 to replace Australian-built Camrys as premium taxis. However, the plan was scrapped and the already imported units were instead sold to the general public.

Toyota unveiled the Mark X saloon in 2004 as the successor to the Mark II saloon which has been on the market since 1968. Instead of being based on a modified Supra chassis "A" series platform, the Mark X shares its platform with the Toyota "S" series platform used under the Crown and Lexus GS.

The continuation of describing this vehicle as the "X" series is a reference to the first dedicated Mark II platform introduced in 1972. Major changes to the Mark series are the engine and footwork. Toyota discontinued the inline-six engines used in the Verossa which included the JZ series and the G series engines, and went to the newly developed GR series engine. Either the 158 kW (212 hp; 215 PS) 2.5 L (2,497 cc) 4GR-FSE or the 188 kW (252 hp; 256 PS) 3.0 L (2,995 cc) 3GR-FSE engine options were available. It was only available at Toyopet Store Japanese locations to position it as a top-level luxury car. The previous top-level car was the Toyota Celsior, which now assumed the more internationally known Lexus LS and was exclusive to Japanese Lexus dealerships.

Both engines offer Dual VVT-i with D-4 direct injection. The rear-wheel-drive models have a 6-speed torque converter automatic gearbox as standard, and the iFour four-wheel drive models have a 5-speed automatic. No manual transmission options were offered.