Mizuho Financial Group, Inc. (株式会社みずほフィナンシャルグループ, Kabushiki-gaisha Mizuho Finansharu Gurūpu), abbreviated as MHFG, or simply called Mizuho, is a banking holding company headquartered in the Ōtemachi district of Chiyoda, Tokyo, Japan. The name "mizuho (瑞穂)" literally means "abundant rice" in Japanese and "harvest" in the figurative sense.

It holds assets in excess of $1.8 trillion US dollars through its control of Mizuho Bank, Mizuho Corporate Bank, and other operating subsidiaries. The company's combined holdings form the second largest financial services group in Japan. Its banking businesses rank second in Japan after Mitsubishi UFJ Financial Group and the 15th in the world by total assets as of March 2017. It is the 90th largest company in the world according to Forbes rankings as of May 2017. Its shares have a primary listing on the Tokyo Stock Exchange.

Mizuho offers a range of financial services, including banking, securities, trust and asset management services, employing more than 56,000 people in 900 offices.

Mizuho splits its business into four distinct divisions, on a global basis:

Mizuho is active in retail banking with 515 branches and over 11,000 automated teller machines (ATMs). Mizuho Bank is the only bank, other than Japan Post Bank, to have branches in every prefecture in Japan. It serves over 26 million Japanese households, 90,000 SME customers, and retail brokerage clients under the name Mizuho Investors Securities nationwide.

Mizuho predecessors, the Dai-Ichi Kangyo Bank (DKB), the Fuji Bank (Fuji) and the Industrial Bank of Japan (IBJ), had great control over many Japanese companies through keiretsu system. The three banks led the DKB Group, Fuyo Group and the IBJ Group respectively. The Fuyo Group traces its history as far back as the old Yasuda zaibatsu. Even now, seven out of ten companies listed on the Tokyo Stock Exchange have dealings with Mizuho.

Former Mizuho Financial Group headquarters (now Otemachi Tower), formerly Fuji Bank head office, in Ōtemachi, Tokyo until 2014

Mizuho Bank head office in Uchisaiwaicho, Tokyo (see also Mizuho Bank Head Office Building)

Mizuho Corporate Bank head office, formerly the Industrial Bank of Japan head office, bordering MHFG HQ in Ōtemachi, Tokyo

Mizuho Securities Co. occupies Ōtemachi First Square, bordering MHFG HQ, in Ōtemachi, Tokyo.

Mizuho was established originally as Mizuho Holdings, Inc. by the merger of Dai-Ichi Kangyo Bank, Fuji Bank, and the Industrial Bank of Japan in 2000.

Mizuho Financial Group, Inc. was established in January 2003 to become the parent company to Mizuho Holdings, Inc. in preparation for its restructuring of businesses. Subsequently, through a share exchange on March 12, 2003, Mizuho Financial Group became the sole shareholder of Mizuho Holdings, which in turn served as the holding company of all of the group's banking and securities units.

On October 1, 2005, all subsidiaries of Mizuho Holdings were transferred to the direct control of Mizuho Financial Group. Mizuho Holdings, no longer a bank holding company, was then renamed Mizuho Financial Strategy, which now focuses on providing advisory services.

Mizuho, through its operations in New York, became involved in the subprime mortgage crisis and lost 7 billion dollars on the sale of collateralized debt obligations backed by subprime mortgages. Its entry was late, in December 2006; it did not participate in gains; only suffered losses. It is the Asian bank which suffered the most losses due to the crisis. The venture into this field has been traced to the employment of Alexander Rekeda, a specialist in this field hired away from Calyon, a unit of Crédit Agricole. Rekeda was made "head of structured credit in the Americas" where he floated several deals that turned toxic. He was later fired and Mizuho shut down its US CDO business. Examples of these included the Aardvark, Tigris, and Delphinius CDOs. The latter two involved the Magnetar hedge fund. Ironically, Calyon had sued Mizuho for hiring away Rekeda and other CDO experts in 2007.