Kobe Bryant's on-again off-again wife, Vanessa, is selling one of the 3 mansions she owns in the Newport Beach area ... and she stands to make a fortune.

The mansion -- which Kobe deeded to her outright in January -- is listed for $3.75 mil ... that's over a million bucks more than Vanessa and Kobe paid back in 2003.

Vanessa's mom, Sofia, has been living in the 6,000 square foot mansion.  We don't know if she's moving in with Vanessa or moving elsewhere.

As for Kobe and Vanessa's relationship, we're told it's like a roller coaster.  So who knows.