The group, which also owns The Philadelphia Daily News and Philly.com as well as The Inquirer, was bought by a group of Philadelphia investors for £562m in 2006. It said that the bankruptcy filing, which is an attempt to restructure its $390m debt, would not affect its daily operations.
Brian Tierney, the group's chief executive, said: "This restructuring is focused solely on our debt, not our operations. Our operations are sound and profitable," referring to operating profits before interest and certain other costs.
The company wants to negotiate with its creditors to rework its debt, which would enable it to focus on its cash flow.
The woes at Philadelphia Newspapers come on hot on the heels of last week's news that The New York Times Company has suspended its first quarter dividend in order to pay off its debt and conserve cash.
In January, Hearst Corporation said that it might shut down 145-year old Seattle Post-Intelligencer newspaper if it cannot find a buyer in 60 days and that a digital-only future was one option being examined. That deadline is fast approaching.
Last week the paper along with the bigger Seattle Times asked US lawmakers for a temporary tax, saying that some of the state's papers are "holding on by our fingertips".
If the Seattle Post-Intelligencer closed it would become the biggest victim of the downturn hitting the US newspaper market. If it went digital, it would be following in the footsteps of the Christian Science Monitor, which in October announced it was scrapping its daily print edition after 100 years and focusing instead on its website.
US media symptoms have also struck north with the news that The Globe and Mail in Canada is to cut its workforce by 10%, resulting in the loss of 90 jobs.