Nearly 30,000 people resigned from the state-supported church last year, 152 people more than in the previous year.
Some of the resignations are attributable to the Freedom of Religion Act which came into effect two years ago.
The reform allows members of congregations to quit straight away, instead of having to wait a month for a resignation to take effect. Resignation can now be done without a personal visit to a district office.
Another reason for quitting could be financial, the Institute said. Members of the Evangelical Lutheran Church have to pay at least one percent of their income in parish tax.
Nearly 85 percent of the Finns are members of the Lutheran Church, one of two state-supported churches.