Bookmakers at William Hill say it's the biggest wager placed on a "yes" outcome so far and.
They believe the customer who is in his 60s and lives in Selkirkshire is involved in the "Yes" campaign and calculate he will bank £32,500 if independence is backed by most voters.
William Hill spokesman Graham Sharpe said: "The previous biggest bet we had taken for a 'Yes' vote was £5000 but the largest wager of all on the outcome so far is £200,000 for a No vote, placed in June this year."
The latest bet has seen the bookmaker shorten the odds from 9/2 to 7/2 for a "yes." vote. However, a "no" vote remaind the favourite outcome at odds of 1/5.