Hedge fund manager John Paulson's gold fund has lost 65 percent so far this year after the portfolio declined 23 percent last month, two people familiar with the fund said on Monday.

Gold had been one of the billionaire investor's winning bets a few years ago but not this year; his investments in gold and gold miners have suffered double digit losses for the past three months.

In June gold tumbled 12 percent in the wake of fears that the Federal Reserve might taper its economic stimulus by cutting its monthly bond purchases.

A spokesman for Paulson declined to comment.

With roughly $300 million in assets, the gold fund is the smallest portfolio in his New York-based firm's lineup with less than 2 percent of its assets and it invests mostly Paulson's personal money, the people familiar with the fund said.

They did not want to be identified because the information is private.

As the heavy losses made for outsized headlines in recent months, Paulson a few weeks ago decided to report the gold data only to the gold fund investors, not to investors in his bigger and better performing funds.

Most of Paulson's bigger funds are in the black this year but the gold investments have weighed on returns of the Advantage Funds, which lost 3.06 percent last month, shrinking the year's gains to 1.17 percent.

Paulson launched his gold fund in 2010, requiring outside investors to commit $10 million each. He hired gold industry experts: Victor Flores, HSBC's former senior gold mining analyst, and John Reade, a former senior metals strategist at UBS. The fund is now called the PFR Gold Fund, in a nod to their last names.