Bill Gross has failed to stem the bleeding in his massive bond fund.

Investors pulled $4.5 billion from Mr. Gross's Pimco Total Return Fund in June, marking the 14th consecutive month of outflows. The exodus continued even as the fund's return has outpaced many rivals during the second quarter.

June's outflow represents 2% of its assets at the end of May and marks the biggest monthly outflow for the fund since September 2013, according to fund tracker Morningstar.

Assets in the flagship bond fund at Pacific Investment Management Co. fell to $225.2 billion at the end of June, compared with $228.9 billion a month earlier. Asset numbers also take into account performance of the fund, while flow numbers don't.

The fund remains the world's biggest bond fund by assets. Mr. Gross is co-founder and chief investment officer at Pimco which manages $1.94 trillion global assets as part of Germany's Allianz SE.

Many investors remain cautious over the Newport Beach, Calif., money manager following a turbulent shake-up of top management in the first quarter along with lagging fund performance and record outflows in 2013.

Write to Min Zeng at min.zeng@wsj.com and Kirsten Grind at kirsten.grind@wsj.com

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