Lindsay Lohan -- CHECK OUT MY SMOKIN' HOT ASS ... It's Bathing Suit Season

Rehab does a body good ... at least for Lindsay Lohan, who strapped on a one-piece bathing suit and flaunted around her 27-year-old physique in Miami today.

It's the first time Lindsay's really shown off her body since leaving court-ordered rehab back in July, stemming from a reckless driving conviction.

Lilo is in south Florida for Art Basel ... which is a huge international art show -- described as the premiere showcase for Modern and contemporary works of art.

For the record, it's 78 in Miami today ... in December.