Joined by his 11-year-old son, Lee told a crowd of about 300 people that he has bought the tabloid in the past - but no more.
And he suggested athletes and entertainers shun the paper's writers because of Wednesday's cartoon, which compared President Obama with a crazed chimp by some interpretations.
"This is not the end," Lee told the demonstrators, who marched in front of the Post's offices near Rockefeller Center shouting, "Shut it down."
"It's not just black folks. It's an insult to everybody."