Mizuho Bank would acquire the stake by the end of this year to leverage the Vietnamese smartphone payment company's retail business, Nikkei Asia reported.
Mizuho wants to tap into Asian growth rates as it's been lagging behind competitors in overseas investment, the paper added.
M-Service, based in Ho Chi Minh City, intends to turn Momo into a "super app" that would allow users access to multiple services.
Back in 2011, Mizuho also invested in Vietnamese state-owned bank Vietcombank. Its new investment in M-Service is expected to strengthen their collaboration in Vietnam's retail market.
Momo has yet to respond to news of the stake acquisition.
The e-wallet currently boasts over 20 million users in Vietnam. In October, it was named the e-wallet with the highest number of users in the country by Decision Lab, a market research firm.