Mr Atsushi Oishi > Mori Hamada & Matsumoto > Tokyo, Japan > Lawyer Profile

Mori Hamada & Matsumoto
TOKYO 100-8222

Work Department

M&A, tax, Private Client / Wealth Management


Admitted in Japan, 1998; New York, 2004. Daini-Tokyo Bar Association; Registered as Licensed Tax Accountant, 2006.




Member of Task Force on Management Buy Out Transactions organised by the Ministry of Economy, Trade and Industry (2007); Member of the Expert Committee on Anti-Tax Haven Legislation and Intangible Assets, organized by the Ministry of Economy, Trade and Industry (2013); Invited researcher at Global Family Business Research Institute, Waseda University (2016-); Member of PB Professional Ethics Review Committee, The Securities Analysts Association of Japan (2018-); Member of PB Education Committee, The Securities Analysts Association of Japan (2018-).


Graduated from the University of Tokyo (LLB, 1996); New York University School of Law (LLM, 2003).

Lawyer Rankings

Japan > Corporate and M&A: Independent local firms

(Leading individuals: Bengoshi)

Atsushi Oishi – Mori Hamada & Matsumoto

Mori Hamada & Matsumoto’s corporate practice is lauded by clients for its ‘extremely high performers‘ and for being ‘reliable in difficult situations‘. Practice heads Hajime Tanahashi and Gaku Ishiwata have specialisms within private equity and venture financing, while the wider practice is able to assist clients with matters such as corporate restructurings, cross-border acquisitions, international mergers, joint ventures, squeeze-out transactions, and shareholder activism. The team, which also includes notable contacts Akira Matsushita and Atsushi Oishi, has a particular strength in the technology sector, as well as experience within the manufacturing, banking, financial services, pharmaceuticals and energy industries. Norihito Sato is commended for providing ‘thoughtful and practical solutions’ for clients.

Japan > Tax: Independent local firms

(Hall of Fame)

Atsushi OishiMori Hamada & Matsumoto

Mori Hamada & Matsumoto‘s tax practice has a particular focus on tax planning, with additional expertise in advising on estate planning for high-net-worth individuals, the tax implications of mergers and acquisitions, and cross-border transactions. The team is jointly headed up by Atsushi Oishi, Makoto Sakai, and Hiroyuki Kurihara, who have significant experience in tax investigations, private wealth management, and tax planning for cross-border mergers and acquisitions, respectively. Clients are also offered tax advisory services by licensed tax accountants, as well as wealth management advice. Hiroshi Oyama is recommended for his work in tax planning and tax disputes.

Japan > Private wealth: Independent local firms

(Leading individuals: Bengoshi)

Atsushi OishiMori Hamada & Matsumoto

In tandem with the firm’s tax practice, the private wealth practice at Mori Hamada & Matsumoto provides a ‘unique‘ one-stop-shop service to its clients, spanning M&A, corporate reorganisations and estate planning. Practice co-head and ‘leading expert‘ Atsushi Oishi advises an extensive client list, including both wealthy individuals and listed and private companies, on cross-border transactions. The firm’s strong litigation practice further bolsters the private wealth team; Makoto Sakai, who leads the team alongside Oishi, has a wealth of experience in tax investigations and tax litigation for high-net-worth individuals and Hiroshi Oyama handles tax disputes, providing ‘accurate and reliable‘ advice. Senior associate Yoshihiko Abe advises high- and ultra-high-net-worth individuals on a range of wealth management planning matters. Promoted to partner in 2023, Koyo Madakoro is a licensed tax accountant who specialises in wealth management. Tax accountant Yuko Maruyama is another name to note.