The fund's monthly performance beat 41 percent of peers, Morningstar data showed. The fund, which has roughly $237 billion in assets, fell 1.92 percent in 2013 after bond prices dropped on fears the Federal Reserve could reduce its monthly bond-buying stimulus.
Gross's fund likely benefited from a rise in Treasuries prices in January, said Todd Rosenbluth, director of mutual fund research for S&P Capital IQ. The fund's largest holding of 45 percent was in U.S. government-related debt as of Dec. 31, according to data on the Pimco website.
Benchmark 10-year U.S. Treasury notes notched their biggest gain in 20 months in January on weaker-than-expected U.S. economic data and after a rout in emerging market assets spurred safe-haven bids.
The yield on the 10-year U.S. Treasury note fell 34 basis points in January to 2.67 percent, the biggest fall in yield since May 2012. Bond yields move inversely to their prices.
(Read more: Hours and friction prompted El-Erian exit)
The Pimco Total Return Exchange-Traded Fund rose 1.66 percent in January, beating 90 percent of peers. The ETF is actively managed and is designed to mimic the strategy of the flagship mutual fund.
Pacific Investment, a unit of European financial services company Allianz SE, had $1.92 trillion in assets as of Dec. 31, 2013, according to the firm's website.
Pimco said last month that chief executive and co-chief investment officer Mohamed El-Erian would depart the company in mid-March, leaving Gross as the sole chief investment officer. The firm has since appointed six deputy chief investment officers to potentially succeed Gross.
(Read more: Pimco's problem: Who cansucceed the 'Bond King'?)
Jeffrey Gundlach's DoubleLine Total Return Bond Fund , a competitor to the Pimco Total Return Fund, rose 2.21 percent last month, beating 99 percent of peers, the Morningstar data showed.
Gundlach is chief executive and chief investment officer of the Los Angeles-based DoubleLine Capital, which had more than $52 billion in assets as of Sept. 30, according to the firm's website.