Yes he did. A brief search of the Mount Vernon Foundation would educate you:
"At the time of George Washington’s death, the Mount Vernon estate’s enslaved population consisted of 318 people. Washington himself had been a slave owner for fifty-six years, beginning at eleven years of age when he inherited ten slaves from his deceased father. "
"Of the 318 slaves at Mount Vernon in 1799, 123 individuals were owned by George Washington and were stipulated in Washington's will to be freed upon his wife's death."
http://www.mountvernon.org/george-washington/slavery/washingtons-1799-will/
"At the time of George Washington’s death, the Mount Vernon estate’s enslaved population consisted of 318 people. Washington himself had been a slave owner for fifty-six years, beginning at eleven years of age when he inherited ten slaves from his deceased father. "
"Of the 318 slaves at Mount Vernon in 1799, 123 individuals were owned by George Washington and were stipulated in Washington's will to be freed upon his wife's death."
http://www.mountvernon.org/george-washington/slavery/washingtons-1799-will/
Ya see what I gotta argue with? :)