The move means Maine is down to two insurers offering plans on the exchange set up under former President Barack Obama's health care law. Anthem this year rolled back its presence in Nevada, California, Ohio, Wisconsin, Georgia and its home state of Indiana.
Anthem in July told state regulators that it covers about 28,700 individuals.
Anthem hinted at its possible departure in June filings. Company spokesman Colin Manning cited a shrinking individual market and uncertainty over a health insurance tax and federal health care subsidies.
Congress has been mulling GOP proposals to repeal and replace the Affordable Care Act, known as "Obamacare." Insurers faced a Wednesday deadline to commit to selling on federal exchanges.
Anthem will reduce its health plan offerings and offer one off-exchange plan available only in Aroostook, Hancock and Washington counties. The insurer had requested double-digit insurance rate increases from state regulators in 2016 and 2017.
Anthem this spring backed a GOP-led health care proposal that ultimately failed to pass the Senate. Joseph Swedish, Anthem's president, chairman and CEO, said it would have continued federal health subsidies, repealed the health insurance tax and allowed the use of tax credits for health plans off the exchange.