By Tim McLaughlin

BOSTON, Jan 30 (Reuters) - Fidelity Investments, one of the largest investors in pre-IPO companies, boosted the value of office space provider WeWork Companies Inc by 53 percent in December, the mutual fund company disclosed on Saturday.

Boston-based Fidelity placed a new valuation on a Series E stake in WeWork that it acquired in June. WeWork's valuation in Fidelity's popular Contrafund was $291.3 million at the end of December, up from $190.9 million in November, the fund disclosed in its latest holdings report.

New York-based WeWork which divides up rented office space for start-ups and small companies. The start-up company is considered a unicorn because it has a valuation of more than $1 billion and has yet to go public. Over the past few years, the valuations of private companies such as Uber, Xiaomi, Snapchat, Pinterest, Airbnb and Dropbox have skyrocketed as they prepare to become publicly traded.

Mutual funds such as Contrafund have become a bigger player in an investing sector once dominated by venture capital firms, boosting competition.

WeWork accounts for just 0.27 percent of Contrafund holdings, which are worth about $110 billion. The fund is run by Will Danoff, who is considered one of the industry's best stock pickers.

(Reporting By Tim McLaughlin)