Bill Gross, manager of the world's biggest bond fund, scooped up Treasury securities for a fourth straight month in January, turning overweight on the debt relative to the fund's benchmark bond index.

Gross, co-chief investment officer at Pacific Investment Management Co., boosted Treasury bonds holdings for a fourth straight month at Pimco's flagship $430 billion Total Return Fund (PTTRX). The holdings rose to 38% of the fund's holdings in January from 30% in December, according to data released on the company's website.

That was more than 35.23% required by the benchmark index--the Barclays Capital US Aggregate Bond Index--at the end of January, a sharp reversal from last year when at one time he completed dumped all of the fund's holdings of Treasurys.

Meanwhile, Gross cut the fund's holdings of mortgage-backed securities to 50% in January, from 48% in December, 43% in November and 38% in both October and September.

After ill-timed bets early last year wagering on price declines in Treasurys, Gross has reversed his strategy over the past few months by buying Treasurys and mortgage-backed securities. The moves reflected his views that the Federal Reserve's unconventional monetary-stimulus programs would keep bond yields, which move inversely to their prices, at relatively low levels.

The fund handed investors a return of 3.46% this year through Wednesday, beating the 0.55% on the Barclays Capital US Aggregate Bond Index. In 2011, stung by the sour bets on Treasurys, the fund posted a return of 4.16%, far below the 7.84% result for the benchmark index.

Pimco, part of Allianz SE (ALV.XE, ALIZF), is one of the world's biggest asset-management companies, with more than $1 trillion in assets under management.

-By Min Zeng, Dow Jones Newswires; 212-416-2229; min.zeng@dowjones.com