The financial services provider sold a two per cent stake in BlackRock to the Japanese firm for an estimated $500 million.
Mizuho is expected to pay $163 per share for an estimated three million shares in the business, the Wall Street Journal reported.
Takashi Tsukamoto, president of the Japanese financial institution, who was quoted by the news provider, said: âThere is more room to cultivate customers in the asset management business if we expand our line-up of global products."
The sale is separate to the 43.6 million shares sold by BofA earlier in the week and a further sale of 5.2 million it is looking to place within the next 30 days.
Barclays Capital, Morgan Stanley and BofA Merrill Lynch are working together on the book running of the sale of the 43.6 million shares.
Mizuho posted an increase in profits for the first six months of the year with figures showing that it more than tripled to 341.76 billion yen ($4.2 billion) from the same period the previous year.
By Jim Ottewill