European football's governing body introduced FFP 'break-even' rules in 2013, requiring clubs to balance their spending with their revenue.
PSG more than doubled the world record transfer fee when they spent 222m euros (£200m) to sign Neymar last month.
They have signed Kylian Mbappe on loan, and could pay £165.7m for him in 2018.
PSG have been owned by the Gulf state of Qatar, via its Qatar Sports Investments fund, since 2011.
The French club made made a profit of 10m euros (£9.2m) on revenue of 520.9m euros (£389.6m at the time of conversion) in the 2015-16 financial year, according to the most recent figures published by Deloitte.
The six-time French champions have failed to meet FFP rules before - receiving a fine, a spending cap and only being allowed to register 21 players for the Champions League in 2014.
Uefa's FFP regulations were approved in 2010 and the first assessments began the following year.
The 'break-even' element states clubs can spend 30m euros more than they earn over a three-year period.
A Uefa statement said the investigation into PSG would "focus on the compliance of the club with the break-even requirement, particularly in light of its recent transfer activity".
It added: "In the coming months, the investigatory chamber of the Uefa club financial control body will regularly meet in order to carefully evaluate all documentation pertaining to this case.
"Uefa considers financial fair play to be a crucial governance mechanism which aims to ensure the financial sustainability of European club football."

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Britain's most decorated Olympian was at Drumchapel Sport Hub in Glasgow as agency sportscotland announced that it had surpassed Holyrood's target of 150 community sport hubs in 2016.
"It's fantastic to see that they've actually committed to this," said Hoy.
"The target is to try to have 200 community hubs open by 2020."
There are now 153 operational hubs across the country with at least one in each of Scotland's 32 local authorities.
Hubs aim to increase the number of people of all ages participating in sport and physical activity across Scotland.
The national agency for sport has also announced a new £6m investment of National Lottery money over the next four years to further develop existing community sport hubs and to help reach the target of new hubs.
Hoy told BBC Scotland: ''The community sports hubs are about the community, providing somewhere that people of all the community, of all ages and all levels of fitness, can come and get fit and have fun - improve their lives basically.
"It's about participation, enjoyment and health, but if we create an Olympic champion off the back of it then all the better."
Hoy, meanwhile, who won six gold and one silver Olympic medals in the velodrome, believes the current British cycling team is looking good ahead of the Rio Olympics.
"The British team are coming on to form at just the right moment," he said.
"They've had a lot of criticism, some of which has been unfounded or a little bit harsh. Teams go through transitions and new riders come in to peak at the right time.
"By definition you're going to be off your peak at others times and I think we should be judged by the performances in Rio."
A knee injury kept Scotland's Katie Archibald from competing for the British team at the World Championships in London this month but she is striving to be fit for Rio, and Hoy certainly hopes that the case.
"Katie is integral to the success of the British pursuit team for the women, and she'll be disappointed that she missed the World Champs," said Hoy.
"But it will fuel that passion and that hunger to work hard and make it to the Olympics.
"They (the women's pursuit team) performed well in the final ride by winning the bronze medal and setting the quickest time they'd ever done before but there's more to come and I think once Katie gets back she'll be firing on all cylinders and she help the team."
Uefa has opened a formal investigation into Paris St-Germain as part of its "ongoing monitoring" of clubs under financial fair play (FFP) regulations.
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Sir Chris Hoy says the commitment shown by the Scottish Government and the National Lottery will help ensure the Commonwealth Games legacy continues.