By Min Zeng

Bond-market heavyweight Bill Gross has warmed up to longer-dated Treasury bonds again after snubbing the securities for months, the latest sign of how the Bank of Japan's bold monetary stimulus is causing global investors to change course.

Mr. Gross, manager of the world's biggest bond fund at Pacific Investment Management Co., said he turned positive on Treasury bonds maturing in 10 years or earlier because the BOJ's aggressive plan to buy Japanese government bonds will drive Japanese investors to seek higher returns in other markets overseas--lifting prices of assets around the world, including U.S. Treasury bonds. The Bank of Japan announced its aggressive easing plan Thursday.

"This BOJ printing seeps out daily into global markets as Japanese institutions which have sold their Japanese government bonds to the BOJ look for higher yielding replacements," said Mr. Gross in an email interview Tuesday afternoon with The Wall Street Journal. "Ten-year Treasurys to us look very low-yielding, but to them they yield 125 basis points more."

Mr. Gross declined to specify whether he has bought 10-year notes over the past few days. For now, Mr. Gross still is staying away from 30-year Treasury bonds, flouting many analysts who argue the longer-dated maturity could be the focus of Japanese purchases as Japanese pension funds and insurance firms need high-quality long-maturity assets to match their long-term obligations.

Mr. Gross runs the $289.1 billion Total Return Fund, and is founder and co-chief investment officer at Pimco. Part of Allianz SE, Pimco is one of the world's biggest asset-management companies, with more than $2 trillion in assets under management.

"In this environment, and ever since 2008, an investor needs to buy what central banks buy before they buy them," said Mr. Gross. "In this case, since it's JGBs, an investor needs to buy what Japanese institutions will buy."

Until recently, Mr. Gross has stayed away from Treasury bonds maturing in 10 years and 30 years. He is worried that these bonds' value would get hit hard if the Federal Reserve's bond-buying program were to taper off, which could cause rates to rise and drive up inflation. He also has fretted about the U.S. dragging its feet to put its fiscal issues in order, a development he has warned may undermine foreign investors' confidence to buy Treasury bonds and the dollar.

Mr. Gross's latest attitude shift suggests he sees the BOJ's stimulus boosting demand for Treasury bonds, keeping bond yields lower in the U.S., not higher as Mr. Gross previously anticipated.

Mr. Gross added that "to a certain extent" planning for what central banks buy is "a guessing game," but historically Japanese investors have bought Treasurys, French government bonds and German government debt. "Of the three, we like Treasurys the best," he said.

Mr. Gross's Total Return Fund (PTTRX) has handed investors a return of 1.22% this year through Monday, beating the 0.55% of the Barclays U.S. Aggregate Bond Index, according to data from fund tracker Morningstar Inc. Over the past 15 years, the fund on average posted an annualized return of 7.2%, compared with 5.9% from the benchmark index.

Subscribe to WSJ: http://online.wsj.com?mod=djnwires