Lil Wayne is putting one of his most prized possessions on the line in order to pay back a $2 million judgment ... his private skate park.

Wayne took out a $1.5 million loan to help pay back the $2 million he owes to a private jet company. According to the docs -- obtained by TMZ -- he's using his Miami skate park as collateral. The good news ... this means Wayne will get to hold on to the $2 million worth of art work cops seized.

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