The decline -- the single largest drop ever tracked by market research firm IDC in a single quarter -- comes as consumers increasingly show a preference for tablets and smartphones.
The decline corresponds to the first full quarter in which Microsoft's latest version of its Windows operating system -- Windows 8 -- was available, suggesting it was getting a cold shoulder from consumers, experts said.
"If you ask most people about Windows 8, they believe it requires a touchscreen," IDC analyst Bob O'Donnell told USA Today. "There are a lot of people who miss the start button."
There were 76.3 million PCs shipped worldwide in the quarter, with sales of desktop computers the weakest, declining nearly in half in the last decade, IDC reported.
Major PC vendors including Hewlett-Packard, Acer and Lenovo all showed sales declines in the quarter, the report said.