Big banks tightened credit for small businesses in June, a month after being their most generous in six years.

But as big banks pulled back, small banks and alternative lenders slightly increased their approval rates, according to a monthly survey of small-business lending released Tuesday by Biz2Credit, an online loan marketplace.

Big banks approved 16.9% of small-business loan applications in June, down from 17.3% in May, which was their highest rate since the survey began in 2007. Small banks approved 49.8% of loans, up from 49.5% in May, while alternative lenders approved 63.4%, up from 63.3% the month before. Small banks approved 50.9% in April, their highest percentage recorded by the survey.

"While approvals dropped slightly at big banks in June, overall small-business lending rebounded in the first half of 2013," Biz2Credit Chief Executive Rohit Arora said in the news release. "Banks, both large and small, are granting loan requests at much higher rates than they did a year ago."

In June 2012 large banks, which the survey defines as those with $10 billion or more of assets, approved 11.1% of small-business loans, while small banks approved 47.5%.

Credit unions have become more selective. They approved 44.8% of loan applications in June 2013, down from 55.8% a year earlier, which was their highest figure since the survey began.

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