Net income for the second-largest bank in the country fell to $979 billion from last year's figure of $1.9 billion.
Among the principal factors behind the decline was bad loan costs, with net interest income falling to $2.1 billion from the year ago period's figure of $2.14 billion.
Meanwhile, income from fees and commissions was also down with trading revenue falling to $115 million billion from $411 million.
During the period Mizuho benefited from the sale of its 4.8 per cent stake in Japanese brokerage Nikko Cordial to Citigroup.
The firm also received fees from the deal through arranging a loan to finance Citigroup's acquisition of Nikko Cordial for $7.7 billion.
Over the last two years, Mizuho has embarked on a period of expansion, through which the number of staff selling investment products and mortgages has doubled.