A block on all language editions of the Wikipedia website was detected at 8:00 a.m. (0500 GMT) on Saturday, monitoring group Turkey Blocks said on its website.
"The loss of availability is consistent with internet filters used to censor content in the country," it said.
When attempting to access the webpage using Turkish internet providers, users received a notice the site could not be reached and a "connection timed out" error.
Monitoring groups have accused Turkey of blocking access to social media sites such as Twitter or Facebook, particularly in the aftermath of militant attacks.
The government has in the past denied that it blocks the internet, blaming outages on spikes in usage after major events. But technical experts at watchdog groups say the blackouts on social media are intentional, aimed in part at stopping the spread of militant images and propaganda.