By Tim McLaughlin

BOSTON (Reuters) - Participants in SunEdison Inc's $155 million retirement plan suffered heavy losses on their investments in company stock last year in the months before the renewable power plant developer landed in bankruptcy.

The retirement savings plan on Wednesday disclosed $10.3 million in losses from investments in 2015. Nearly all of that came from investments in SunEdison stock, according to the retirement plan's annual report.

SunEdison filed for bankruptcy in April after an aggressive growth plan proved unsuccessful. Last month, SunEdison received final bankruptcy court approval of debtor-in-possession (DIP) financing in the form of new capital totaling up to $300 million.

At the start of 2015, about $17 million, or 13 percent of the retirement plan's $133.1 million in total investments, was held in SunEdison stock, according to the annual report.

SunEdison shares plunged 75 percent in 2015 as the company signaled troubles from its heavy debt load. The stock traded at 14 cents a share on Wednesday.

By the end of 2015, the plan had $155.5 million in net assets available for benefits, but only $5 million of that was in SunEdison stock.

The plan's assets increased from the previous year, largely from new contributions from SunEdison and participants.

In March of this year, SunEdison delivered a blackout notice that prevented retirement plan participants from investing their contributions in the SunEdison stock fund. The notice also prevented them from transferring any amount from other investment options, such as mutual funds, into company stock, according to the annual report.

(Reporting by Tim McLaughlin; Editing by Will Dunham)