Attorney General Martha Coakley says she wants to know if the schools misled students about the cost of coursework and the odds of finding jobs in their field after graduation, the Boston Globe reported Sunday.
Coakley expanded her investigation after looking into a handful of schools two years ago.
"The more we look, the more we see it as a real problem," she said. "This has potential to be a predatory business."
Massachusetts has at least 136 for-profit schools.
Other states have launched similar investigations. Jack Conway, Kentucky's attorney general, has sued four schools. He is leading a group of 30 state attorneys general probing the industry.
Government officials say some for-profit schools, which typically charge more than public and non-profit schools, get 90 percent of their funding from federal student aid. Students are left with much higher debt they may not be able to repay, leaving taxpayers on the hook.