By Jennifer Ablan

NEW YORK (Reuters) - Investors put $10.2 million into Bill Gross's Janus Global Unconstrained Bond Fund in March, reversing cash withdrawals from the previous month, Morningstar said on Thursday.

The Janus Global Unconstrained Bond Fund, which suffered cash withdrawals of $18.5 million in February, had assets under management of $1.5 billion at the end of March. That's up from $1.46 billion at the end of January, its previous high in net assets, according to Morningstar data.

"The Janus fund has started 2015 off well - up 2 percent in the first quarter is encouraging," said Todd Rosenbluth, director of ETF & Mutual Fund Research at S&P Capital IQ. "As the fund establishes a longer record we think investors will pay more attention."

Flows to Gross's new fund have been choppy. After taking in $770 million in November, the fund had net deposits of $176 million in December and just $85.6 million in January, according to Morningstar data.

In January, Janus Capital Chief Executive Dick Weil said on a conference call that Gross had pumped more than $700 million of his own money into the fund.

Gross, who built Pimco into one of the largest investment firms in the world, resigned from the firm Sept. 26 to join Janus Capital Group Inc. A Janus spokeswoman declined to comment.

Since Gross took over the Janus Global Unconstrained Bond Fund on Oct. 6, the portfolio is beating 73 percent of its peers, Morningstar added.

Unconstrained bond funds had become some of the most popular investment vehicles over the last year because they have the flexibility to invest in all types of bond securities globally and often choose credit rather than interest-rate sensitive assets.

The strategy has come into question, however.

"I think the slow pace of inflows reflects the uncertainty investors have about unconstrained bond funds because they've been designed to get ahead of rising interest rates which we have not seen at all," said Jeff Tjornehoj, head of Lipper Americas Research.

Since the end of August, the JPMorgan Strategic Income Opportunities fund has had outflows of $5.4 billion and the Goldman Sachs Strategic Income Fund has had outflows of $2.7 billion since the end of November, according to Lipper.

"Much larger and better-known peers have been struggling with outflows for months," Tjornehoj said.

(Reporting By Jennifer Ablan; Editing by Chizu Nomiyama, Bernard Orr)