Officers raided a workshop in the port of Izmir, where they say they found life jackets stuffed with packaging rather than buoyancy aids.
The four workers making the jackets included two young Syrian girls.
On Tuesday, the bodies of 34 migrants were found along Turkey's coast. Many were wearing life jackets.
Several children were among the dead.
More than one million migrants crossed the Mediterranean in 2015 and the vast majority went from Turkey to Greece.
Many migrants buy life jackets to help them survive the dinghy journey. A properly made jacket costs up to a £100 (€130; $150), reports the BBC's James Reynolds in Istanbul.
But many migrants make do with cheaper, badly made ones, which cost just £10 and may offer no protection whatsoever, our correspondent says.
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According to the UN, 3,771 people were listed as dead or missing in 2015.
In Wednesday's raid the authorities seized 1,263 life jackets that failed to correspond to safety standards, Turkey's Dogan news agency said.  The workshop was in the centre of Izmir, a major hub for refugees and migrants.
Four people were found working in the workshop, including two young Syrian girls, the news agency said. It did not publish the girls' ages.
The confiscated life jackets have been sent to the local police for examination and an investigation has been launched.
It comes one day after the bodies of more than 30 migrants were washed up in Turkey. Their boats capsized in bad weather on the way to the Greek island of Lesbos, the authorities say.
Turkish media published harrowing images of the corpses, many still wearing life jackets that had apparently been of no use.
Migrants are continuing to arrive on the Greek islands every day, despite the wintry weather. Lesbos is by far the most popular destination for migrants leaving Turkey. More than 500,000 reached the island in 2015.
Late last year, Turkey reached a deal with the European Union to tighten its borders and reduce the numbers crossing to Greece in return for €3bn (£2.1bn) and political concessions.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.
Police in Turkey say they have confiscated more than 1,000 fake life jackets made for migrants wanting to cross the Aegean Sea to Greece.